Vests aren't just for golfing anymore! Whether you call them vests, tank tops or shells, these 'sweaters' will keep you warm, while keeping you cool!
If you're a beginning knitter - or just want to try your hand at a new technique - sleeveless sweaters are a great way to start. The main benefit is that you don't have to sew the sleeves in... and many patterns will actually instruct you to knit up to the armholes on a circular needle (in a tube), so you won't even have to sew those seams!
Good fit for a vest is crucial. Personally, i look through the closet and find a vest that fits me perfectly. I then lay the vest on my bed, flatten it out nicely, and measure from underarm to underarm. If you then double that measurement, you'll get the optimal finished chest size (which you'll then match to the pattern).
In the past, I've knit sleeveless tops that were too open in the underarm area (i.e., the armhole was too big). To remedy the problem, i ended up pulling out the crochet hook and creating a few single crochet rows around the armhole. Once, i used a contrasting color (& did the same on the neckline and at the bottom) & got tons of compliments -- another example of Creativity Born from Mistakes :)