http://sourceforge.net/projects/ultrastar
http://sourceforge.net/project/scree...roup_id=116377
Singstar for the PS2 is a great game for parties. Sadly, it's not available for the PC. But that has changed, since there is a freeware clone of Singstar on the PC: Ultra Star. It's still work in progress, but it's already a lot of fun. Try it!
The demo version comes with a single song, but there are already some people writing their own songs you can download and sing.
http://www.ultra-star.de.vu/ (german)
http://ustar.prv.pl/ (polish, you gotta register in order to download)

You think the game lacks a special song? Convert it yourself.
http://www.10c-chaos.de/phpBB2/viewtopic.php?t=58
This tutorial is only in german though, maybe someone finds an english one.

Have fun!