Jailbreak your iOS 4.2.1, 4.2 or 4.1 mobile device with Redsn0w 0.9.6b4!
One catch: If you're using an iPhone 4, 3GS (new boot ROM), iPad, iPod Touch 3g or 4g, this will be a tethered jailbreak. That is, you'll need to rejailbreak your iOS device every time your battery dies. Which is a bummer. But, hey, jailbroken iPhone/iPod/iPad!
To follow along, you'll need to download the latest version of Redsnow.