My favorite way to look like I've lost a few pounds without hitting the gym? Shapewear, especially tummy-slimming camis that give you a sleek look (especially under knits where lumps and bumps really show.)
I like the Barely There camisole -- I chose the side-shaping version but there are others available -- because it felt firming without being restrictive. It gives me a smoother line under knits and is short enough to wear under T-shirts. Best of all, the price is right: most versions are less than $20.
The advantage to Yummie Tummi's shapewear is that the cotton tanks have a tummy-smoothing inset, but otherwise look just like a regular cotton cami. That means you can wear these under a jacket, cardigan or shirt just like you would a regular tank top, but get the benefits of tummy-smoothing shapewear.