Try
VanillaWallet (I'm the developer). It's a simple Bitcoin wallet that's easy to use. It stores its files in the same directory as the program, which makes it good for portability on USB drives. It's a light-weight client, which only has to store the block-chain headers -- that means that the block store file is only about 20MB.
I currently call it Alpha, but it's fully-functional and has been entirely stable for me (read the caveats). I'd love to get more feedback on it, so please let me know how I can make it suit your needs!
You're situation is exactly what VanillaWallet is all about!