I'm a big fan of an English bitter.
I also like a Session IPA/India Session Ale for summertime. You can add all your hops at whirlpool and get tremendous hop aroma with a moderate amount of bitterness.
Mmm, Pilsner is a good one too.
Saison is good any time of year, and a Witbier seems to work well in the summertime. So is a Berliner Weiss.
Summer is definitely one of my top four seasons for beer drinking.