JailbreakMe 2.0 Star is the userland jailbreak for iPhone 4, iPhone 3GS, 3G on iOS 4 / 4.0.1, iPod touch on iOS 4, and iPad on iOS 3.2.1 is out. It is a browser based jailbreak, all you have to do is to browse to www.jailbreakme.com from your iOS device to jailbreak it.

See here on how to jailbreak your iPhone 4.

Complete list of supported devices include:

iPod 1G on 3.1.2
iPod 1G on 3.1.3
iPod 2G on 3.1.2
iPod 2G on 3.1.3
iPod 2G on 4.0
iPod 3G on 3.1.2
iPod 3G on 3.1.3
iPod 3G on 4.0
iPad on 3.2
iPad on 3.2.1
iPhone 3G on 3.1.2
iPhone 3G on 3.1.3
iPhone 3G on 4.0
iPhone 3G on 4.0.1
iPhone 3G[S] on 3.1.2
iPhone 3G[S] on 3.1.3
iPhone 3G[S] on 4.0
iPhone 3G[S] on 4.0.1
iPhone 4 on 4.0
iPhone 4 on 4.0.1