The iPhone Dev Team has released a simple-to-use GUI tool that allows you to unlock your iPhone for use with any SIM. The tool, which is based on their previous command-line work, provides one-touch speedy unlocking. This is a big improvement on the first generation release. It no longer requires you to use special files or to dump nor data.
Find out more at the #iphone channel at irc.osx86.hu. Remember, this is early software and unstable. If risk isn't your thing, you'll probably want to wait a few days or weeks for things to stabilize.
Update: After reports of failed unlocks, Sam has updated the version to fix a timing issue. Current version is now 1.0.1, which solves the timing issue.
Update 2: I know of a youtube hack and have heard third-hand of a Visual Voicemail hack. Will post when I have details.