The actor who played "Colby" is Tyson Ritter, who is also the lead vocalist for the rock band The All-American Rejects. If you listen closely you'll hear one of his band's songs playing in the background of nearly every scene he appears in.
During Oliver and Shelley's date, she tells him that when voting she would not take Simon's opinion into consideration, but would listen to Paula and Randy. This is a reference to American Idol (2002), a reality show in which Katharine McPhee was runner-up after contesting.
When Lily is going to mail out the invitation envelopes to future Zeta members, the boy that distracts her says his name is Cole Trickle - which is the name of the character played by Tom Cruise in Days of Thunder (1990).