here are the social networking sites which allow DoFollow
Its a great way to increase you pagerank by having your links on them ;) :D
A1WebmarksPR5
BibsonomyPR7
BlogHopPR5
ClipClipPR5
ComplorePR4
DiigoPR5
FavesPR0
FurlPR7
info4itPR3
JumptagsPR6
KapelyPR3
ListiblePR5
Mister-WongPR7
MyLinkVaultPR5
MyPIPPR3
MyVmarksPR5
OnMyListPR4
PlimePR5
SearchlesPR6
SlashdotPR9
SpurlPR6
SyncOnePR3
UnalogPR6
UPCHUCKrPR0
YattlePR2