CrunchFund - 3 (Stamped, GoPollGo, Tumblr)
True Ventures - 3 (OnTheAir, Snip.It, Lexity)
Khosla Venture - 3 (Snip.It, Xobni, Rockmelt)
SV Angel - 3 (Snip,It, Xobni, Rockmelt)
Google Ventures - 2 (Astrid & Stamped)
Spark Capital - 2 (Tumblr & Lexity)
Jack Herrick - 2 (Qwiki & Astrid)
Greylock - 2 (Tumblr & Qwiki)
First Round Capital - 2 (Xobni & Rockmelt)
Also to note, Lexity & Jybe were founded by former Y! employees.