Roy,

It depends upon how much you want to spend.  I spend about 140 dollars on
the diamond dual band antenna which has 6 db gain on 2 meters and 8 on the
450 band.  It is 8.5 feet tall.  I recently just purchased their 24 foot
tall dual band antenna and spent 400 dollars for it.  It has 9.3 db gain on
two meters and 13 db gain on the 450 band.  You can log on to r and l at
http://www.randl.com
and find all sorts of verticals for a lot less money which are dual banders.
In fact, they sold the 400 dollar diamond antenna I purchased for about 75
dollars less.  Unfortunately, when I wanted to buy, they were sold out, of
course.

73,
Phil.
k0nx