How to upgrade rooted HTC Desire with Unrevoked3 (Clockworkmod) to Froyo 2.2?
If you have succesfully rooted the phone and have the ClockworkMod recovery image, you can easily flash a custom 2.2 ROM.

Have a look on MoDaCo for some good options. You should also install the Rom Manager app from the market for easy flashing, booting to recovery, backups, etc.

You shouldn't have to wait long before there are plenty of 2.3 options too :) (there are a couple already on the XDA forums, but these are very new so you might want to wait just a little while whilst all the kinks are ironed out).