Twitter-to-FriendFeed Contact Sync is a simple, but useful tool to find Twitter buddies who are on FriendFeed. If you're considering FriendFeed, this is a great way to automatically populate your subscriptions list with people you may already be following elsewhere.
It works by tapping into your Twitter friends list and cross-referencing your follows with FriendFeed users. By giving it your FriendFeed nickname and API key (which can be found here), it will provide you with simple one-click subscription buttons that can be clicked without taking you off the page.
In case you're hesitant about giving out your security credentials for two different services, worry not. That app simply uses them for that single session authentication after which they're wiped clean from the server. In fact, a simple refresh of the page clears everything.