Probably Sudafed, or any generic version of it. It's one of the few medications you can safely take while pregnant. That said, the long term effects of any metabolism boosting substance on the heart, etc., are probably not great.
The best thing for the less food-disciplined may be to follow the NoS plan ( http://www.nosdiet.com/ ).
Sudafed no longer uses pseudoephedrine in its products because it was being used to synthesize meth. It now uses phenylephrine, which does not have an appetite suppressing effect.
I only happen to know about pseudoephedrine's appetite suppressing side effect because of terrible allergies. For years I hated eating, until medications stopped including it as the active ingredient.
You can get the "old formula," in most states, but they keep it behind the counter and you need to hand over your driver's license to be scanned. I only happen to know that because the phenylephrine doesn't work anywhere near as well for me when I have a cold.
Dexatrim comes to mind. (As does any Pseudoephedrine carrying drug)