HTC is our favorite handset maker because their devices have traditionally been the most hackable. As Motorola put it, if you want an Android phone for experimenting with Android system development and re-flashing custom ROMs, then buy HTC.
Google and Sprint handed out 5,000 HTC EVO 4Gs at Google I/O and it only took a few hours effort for developers to gain root access to the device. The three person team of Matt Mastracci, ozzeh, and Joshua Wise have released a few screens and videos of their hack, but have yet to detail the process.
This hack is worth mentioning because the EVO does not go on sale till June 4th. The device will ship with Android 2.1, but at this rate I would not be surprised if the development community back-ports Android 2.2 months before HTC sends out their official release. Google has yet to release the source code for Android 2.2, so it could be a few weeks, but keep an eye out for an upcoming release.