HTC has released kernel sources for the Rezound, Explorer, and the EVO Shift 4G update for developers to have a play with. In addition, they have let loose the full Desire Gingerbread update for developers and users alike. The kernel source won't be as useful to the average user as it will be for folks who hack away at building their own kernels and custom ROMs, but in the end it's us users who get the most benefit -- we all know custom builds rock.
HTC didn't stop at kernel source though. They have also released the full HTC Desire 2.3 update, making it available for download and flashing. If you remember, the Gingerbread build for the Desire had to get pretty stripped down in order to fit everything into the 512MB of ROM space. Originally HTC had stated that they wouldn't be updating the Desire, but that didn't go over very well with users.
If you're looking for any of these goodies, hit the source link where you'll find a handy list of downloads.