If you want a quick throwaway wallet use a site like blockchan.info. Not only are your funds in your actual account(not consolidated into some giant wallet), but the private key is never revealed to the server. They could not take your coins even if they wanted to.

Take a backup of the unencrypted keys from blockchain.info and you can import them into any client if the site goes down.

You should be on the watch for their javascript changing though.