Here's some more references from Medline:

 Thorogood M.  Mann J.  Appleby P.  McPherson K.
  Department of Public Health and Policy, London School of Hygiene and Tropical
  Medicine.
  Risk of death from cancer and ischaemic heart disease in meat and non-meat
  eaters [see comments].
  BMJ.  308(6945):1667-70, 1994 Jun 25.
  OBJECTIVE--To investigate the health consequences of a vegetarian diet by
  examining the 12 year mortality of non-meat eaters and meat
  eating controls. DESIGN--Prospective observational study in which members of
  the non-meat eating cohort were asked to nominate friends or relatives as
  controls. SETTING--United Kingdom. SUBJECTS--6115 non-meat eaters identified
  through the Vegetarian Society of the United Kingdom and the news media (mean
  (SD) age 38.7 (16.8) years) and 5015 controls who were meat eaters (39.3
  (15.4) years). MAIN OUTCOME MEASURES--Standardised mortality
  ratios for cancer, ischaemic heart disease, and total
  mortality in the two cohorts and death rate ratio in the
  non-meat eaters compared with meat eaters after adjustment for potentially
  confounding variables. RESULTS--Standardised mortality
  ratios (taking the value among the general population as 100) for ischaemic
  heart disease were 51 (95% confidence interval 38 to 66) for meat eaters and
  28 (20 to 38) for non-meat eaters (P < 0.01). Values for all cancers were 80
  (64 to 98) and 50 (39 to 62) for meat eaters and non-meat eaters
  respectively. After adjustment for the effects of smoking, body mass index,
  and socioeconomic status death rate ratios in non-meat eaters compared with
  meat eaters were 0.72 (0.47 to 1.10) for ischaemic heart disease and 0.61
  (0.44 to 0.84) for all cancers. CONCLUSIONS--The reduced
  mortality from cancer among those not eating meat is not
  explained by lifestyle related risk factors, which have a low prevalence
  among vegetarians. No firm conclusion can be made about deaths from ischaemic
  heart disease. These data do not justify advice to exclude meat from the diet
  since there are several attributes of a vegetarian diet apart from not eating
  meat which might reduce the risk.

  Chang-Claude J.  Frentzel-Beyme R.
  Division of Epidemiology, German Cancer Research Centre, Heidelberg.
  Dietary and lifestyle determinants of mortality among German
  vegetarians.
  International Journal of Epidemiology.  22(2):228-36, 1993 Apr.
  Lifestyle characteristics of a cohort of 1904 Germans adhering mainly to a
  vegetarian diet were examined in relation to their mortality
  after 11 years of follow-up. Poisson regression modelling was performed to
  consider the simultaneous effects of different variables on
  mortality from all causes, cancer (ICD 140-208) and
  cardiovascular diseases (ICD 390-459). Compared to a low level of
  self-reported physical activity, those with a medium or high level of
  activity experienced only half the mortality from all causes
  and from cardiovascular diseases. Physical activity showed no beneficial
  effect for cancer mortality in this cohort. The body mass
  index (BMI) was an independent risk factor for mortality
  among men but essentially unrelated to mortality among
  women. Those in the middle third of the BMI distribution experienced the
  lowest mortality. A negative association between BMI and
  cancer mortality lost statistical significance when the
  first 5 years of follow-up were deleted, suggesting that a lower BMI was a
  consequence of prevalent disease. Both the duration of
  vegetarianism and the vegetarian status (strict versus
  moderate) showed a moderate effect on all cause and cancer
  mortality. A longer duration of
  vegetarianism (> or = 20 years) was associated with a lower
  risk, pointing to a real protective effect of this lifestyle. A lower risk of
  death among moderate vegetarians suggests that sound nutritional planning may
  be more important than absolute avoidance of meat.

  McMichael AJ.
  Vegetarians and longevity: imagining a wider reference
  population [editorial; comment] [see comments].
  Epidemiology.  3(5):389-91, 1992 Sep.

  Chang-Claude J.  Frentzel-Beyme R.  Eilber U.
  Department of Epidemiology, German Cancer Research Center, Heidelberg.
  Mortality pattern of German vegetarians after 11 years of
  follow-up [see comments].
  Epidemiology.  3(5):395-401, 1992 Sep.
  A cohort of 1,904 vegetarians and persons leading a health-conscious
  life-style in the Federal Republic of Germany was identified in 1978. After a
  follow-up of 11 years, mortality from all causes was reduced
  by one-half compared with the general population [the standardized
  mortality ratio (SMR) was 0.44 for men, 0.53 for women].
  Among the 858 men, 111 deaths were observed, with 255 expected; among the
  1,046 women, 114 deaths were observed, with 215 expected. The lowest
  mortality was found for cardiovascular diseases (SMR = 0.39
  for men, 0.46 for women); in particular, for ischemic heart diseases,
  mortality was reduced to one-third of that expected. Cancer
  mortality was reduced by one-half in men (SMR = 0.48), but
  only by one-quarter in women (SMR = 0.74). The deficit in cancer deaths was
  mainly observed for lung cancer and gastrointestinal cancers in males and for
  gastrointestinal cancers in females. Deaths from diseases of the respiratory
  and digestive systems were also reduced by about 50%. An excess of deaths
  occurred only for anemia. When the strict and the moderate vegetarians were
  analyzed separately, the strongest differential was found for ischemic heart
  diseases, which were much less frequent among strict vegetarians for both
  sexes. Some nondietary factors, such as higher socioeconomic status, virtual
  absence of smoking, and lower body mass index, may also have contributed to
  the lower mortality of the study participants.

  Lindsted K.  Tonstad S.  Kuzma JW.
  School of Public Health, Loma Linda University, CA 92350.
  Body mass index and patterns of mortality among Seventh-day
  Adventist men.
  International Journal of Obesity.  15(6):397-406, 1991 Jun.
  This study examines the relationship between body mass index (BMI) and
  26-year mortality among 8828 nonsmoking, nondrinking
  Seventh-day Adventist men, including 439 who were very lean (BMI less than 20
  kg/m2). The adjusted relative risk comparing the lowest BMI quintile (less
  than 22.3) to the highest (greater than 27.5 kg/m2) was 0.70 (95 percent CI
  0.63-0.78) for all cause mortality, 0.60 (95 percent CI
  0.43-0.85) for cerebrovascular mortality, and 0.80 (95
  percent CI 0.61-1.04) for cancer mortality. Very lean men
  did not show increased mortality. To assess whether the
  protective effect associated with low BMI is modified by increasing age, the
  product term between BMI and attained age (age at the end of follow-up or at
  death) was included as a time-dependent covariate. For ischemic heart disease
  mortality, age-specific estimates of the relative risk for
  the lowest quintile relative to the highest ranged from 0.32 (95 percent CI,
  0.19-0.52) at age 50 to 0.71 (95 percent CI, 0.56-0.89) at age 90.
  Interaction was also seen for the next lowest quintile (22.4-24.2). There was
  a significant trend of increasing mortality with increasing
  BMI for all endpoints studied. For cancer and cerebrovascular
  mortality the P-values for trend were 0.0001 and 0.001
  respectively. For the other endpoints the P-values were less than 0.0001.
  Thus, there was no evidence for a J-shaped relationship between BMI and
  mortality in males. While the protective effect associated
  with the lowest BMI quintile decreased with increasing age for ischemic heart
  disease mortality, it remained greater than one at all ages.
  The relatively large number of subjects who were lean by choice, rather than
  as a result of preclinical disease or smoking, may explain these findings.

  Dwyer JT.
  Tufts University School of Medicine, New England Medical Center Hospital,
  Boston, MA 02111.
  Health aspects of vegetarian diets. [Review] [342 refs]
  American Journal of Clinical Nutrition.  48(3 Suppl):712-38, 1988 Sep.
  Recent studies of vegetarian diets and their effects on morbidity and
  mortality are reviewed. Vegetarian diets are heterogeneous
  as are their effects on nutritional status, health, and
  longevity. Mortality rates are similar or
  lower for vegetarians than for nonvegetarians. Risks of dietary deficiency
  disease are increased on vegan but not on all vegetarian diets. Evidence for
  decreased risks for certain chronic degenerative diseases varies. Both
  vegetarian dietary and lifestyle practices are involved. Data are strong that
  vegetarians are at lesser risk for obesity, atonic constipation, lung cancer,
  and alcoholism. Evidence is good that risks for hypertension, coronary artery
  disease, type II diabetes, and gallstones are lower. Data are only fair to
  poor that risks of breast cancer, diverticular disease of the colon, colonic
  cancer, calcium kidney stones, osteoporosis, dental erosion, and dental
  caries are lower among vegetarians. Reduced risks for chronic degenerative
  diseases can also be achieved by manipulations of omnivorous diets and
  lifestyles. [References: 342]