Just taking a look at the UCB schedule for June and July and it looks quite tasty. Here a few shows that I think are worth seeing:

Michael Ian Black: I Am A Wonderful Man – June 26th, 2007 @ 7:00 PM
Matt Besser’s Magical Sack of Dump – July 25th, 2007 @ 8:00 PM
UCB In Central Park – Hosted by Human Giant and featuring Demetri Martin, The Difibulators, Slovin & Allen, Rebecca Drysdale, Reggie Watts, Stickerbook, and Cracked Out.
Inside Joke with Matt Besser, Ian Roberts, and Matt Walsh – July 26th, 2007 @ 8:00 PM
Scheer and McBrayer @ FIT – July 28th at 7:00 PM
Daily Show Colbert Report Improv Jam @ FIT: Featuring Dan Bakkedahl, Peter Grosz, Peter Gwinn, Ed Helms, Laura Krafft, Rob Riggle and more. – July 28th at 7:00 PM
Horation Sanz and the Kings of Improv @ FIT – July 28th at 7:00 PM
The 9th Annual Del Close Marathon – July 27th – 29th