...I use a lot of seamless patterns for Posette clothes, in our free stuff page there are those of TdaC , and there are those from Queri at PoserPros:
http://www.poserpros.com/forums/viewtopic.php?t=9114&highlight=
(search for Queri in their free stuff forum)
It seems that exist a specific program to make seamless patterns, I'll search for it...