A suggestion is to look for shows that you may not have given a chance to fall into your regularly watched programs. Since most everything during summer are re-runs you'll be able to catch shows that you normally wouldn't watch.
Another idea is to take a look at shows that are being released to DVD. Following is a list of some good shows to check out if you haven't already seen them.
DVD Releases June 6th, 2006
He-Man and the Masters of the Universe - Season 2 Vol. 1
Navy NCIS: Naval Criminal Investigation Service - Season 1
DVD Releases June 13th, 2006
Dharma and Greg - Season 1 DVD
Beavis and Butt-head - The Mike Judge Collection Vol. 2
Stargate SG-1 - Season 1-8 Slim Sets
For a full list of release dates check out TVShowsOnDVD.com.