Though it's almost impossible to find an HP TouchPad at this point (at a reasonable price, anyway) the Android mod community is still rolling full steam ahead on the abandoned platform. Though the MIUI version of Android isn't as far along as CyanogenMod 7 for the TouchPad, it's reached the beta stage first, aftera short alpha introductory period. You can download MIUI for the TouchPad over at RootzWiki.
MIUI brings its distinctive UI to the HP hardware, which is appropriate enough, since in many ways it resembles HP's WebOS as far as visual style goes. The ROM is mostly functional, with just a few bugs including MIUI's standard Launcher2 modification. GO Launcher is included in the beta ROM as an alternative. The menu system is a little tough to work with the TouchPad's single iPad-style button, but downloading SoftKeys or Button Savior should fix things right up. Beyond that, everything seems to be working properly, including MIUI's theme engine. You can flash the ROM via ClockworkMod, just like CyanogenMod.
There's been a surprising amount of news in the TouchPad world lately. Since HP's nobly decided to open source WebOS, you should start seeing some heavily customized versions of the TouchPad's original software very soon, and perhaps a few ports to Android hardware. Even so it's a sad end - WebOS was a solid and extremely friendly operating system, even if the developer support never materialized. Just yesterday we got a solid look at the unreleased 7-inch TouchPad Go, which revealed it to be a surprisingly awesome little tablet.