I'm not crazy about my upper arms either, but am vowing to work on it.
In the meantime, I really appreciated Angie's recent blog post...suggesting that *now* is the time to buy easy/breezy/cool-ish tops (if you're in North America) that actually have sleeves before the onslaught of nothing but sleeveless:
http://youlookfab.com/2012/02/.....ered-tops/
It's a good idea, don't you think?
That said, I have noticed that certain sleeveless tops and dresses seem to work better for this problem - and these are the tops that have wider shoulder coverage. The other thing I've noticed is that super-short sleeves are actually worse than sleeveless tops in many cases. Long story short is that a sleeveless top that isn't a spaghetti strap type of top is actually a lot more flattering than a top with those cap sleeves that cut off the arm at it's most unflattering point.
Examples of sleeveless tops that look a whole lot better than you'd expect:
http://www.anntaylor.com/ann/p.....Color=1035
http://shop.nordstrom.com/s/th.....tback=1925
If it's the height of summer where you are - don't despair - you really can wear sleeveless tops, despite feeling weird about arms. It's just a matter of choosing tops and blouses that have substantial shoulders and no sleeves, rather than tops that have teensy shoulder straps or tops that have super short sleeves that bisect upper arms at an unflattering point.
Don't give up on cooler tops - there *are* sleeveless tops that can work, it's just that you don't want something skimpy. You might be surprised to find that sleeveless tops can be quite flattering on less-than-perfect arms. Too-short sleeves (cap sleeves, those flutter-type sleeves) can sometimes be worse than something sleeveless.
Go ahead and try some sleeveless tops - just be sure to go for things that have decent shoulder coverage and not super-skimpy straps. You might actually find that some of these are quite flattering. I know it seems counterintuitive, but it's true.
Hang in there and here's hoping you find some summer tops that you feel great in *and* that help you keep cool.