I really like MultiBit,

It's only ~40mb with the blockchain downloaded. (It downloads a heavily stripped down version of the entire chain, and goes back for information on addresses it actually manages)
It doesn't rely on an external server to host the blockchain (like Electrum)

And it allows you to manage multiple wallet files so you can export only certain keys and use them on multiple devices (for petty cash on a phone, as an example. If you lose the phone, you already have the wallet open so you can move the coins out of it.)