I have searched the web trying to find out where you can get NXT-G blocks (now that NXTasy has failed)
Old NXTasy Repository
Some blocks are available here and here , but they don't have descriptions and are not sorted.
The Legacy Blocks, Mini Blocks and the Color Lamp & Color Sensor blocks are available from the official LEGO Education site
Some blocks are available from the Team Hassenplug site
Michael Gasperi's Homebrew NXT-G Blocks
Third Party Sensor blocks HiTechnic and Mindsensors
I still need the Music Box block- Used to be available from Avid Programmer (what happened to that site anyway?!)
If you have the ZIP files of blocks that are not available from the links, could you please attach them. If you have deleted the ZIP file but you still have the blocks in your palette you can recover the ZIP files with the Block Import and Export wizard- Just click on the 'Manage' tab, select the block you want and click on export. LINK
EDIT: Most blocks now available here- http://box.net/mindboards/
Block tutorials coming soon to here- http://nxtguide.webs.com/
Note: Edits are in red.