SlimFast sux... just make sure you don't get too much carbs in and have enough protein.
If you're looking for a Meal Replacement Product you'd better look into the bodybuilding supplements... I can recommend "Infusion" by S.A.N. very tasty and awesome nutrtional value...
get it @
http://www.heavyweights.net
(no spam just a site I know is reliable)