Hi!
I did the trial for Pocket Diet Tracker & Pocket Diet
http://www.electricdreams.ca/products.htm and I was happy enough with Pocket Diet Tracker to purchase it without trying out all of the other possibilities.
RMRDiet (PPC)
http://www.rmrsoft.com/ipaq/diet.htm would probably have been my next choice of things to try. Here are some others:
MyBody Suite for Pocket
http://www.l3solutions.com/L3Prod_L3MBPPC.htm
Pocket Health by Delta Software
www.delta-sw.com/health.html
And I am sure that there are many more.