There is a product called CHREESE, it is a dry mix in packets kind of like
gravy, and has several variations (mozzeralla type, cheddar type, etc.).
It is especially good for making a macaroni & cheese type dish but can be
used for many other things, including sandwich "melts", pizza, etc.  You
make it by adding boiling water and dairy-free margarine or olive oil and
mixing in a food processer or blender.  I would say that the cheddar one
could make a good velveeta substitute.  Come to think of it, they also
make chreese dips, which come in jars, that might be even better but I've
never tried those.  Made by Road's End Organics, www.chreese.com

Re: the cream soups, I often substitute with a white sauce I make myself.
Just melt 2-3T dairy-free margarine over med-low heat, then whisk in 1-2T
flour and a pinch of dry mustard, then add about 3/4 cup of plain or
unsweetened soy milk and cook over medium heat until thickened.  You can
also do this in a skillet after cooking something else (such as veggies)
by melting the margarine and then adding the soy milk, then stirring in
some arrowroot to thicken.  Season to taste.