The beach bars are reopening this weekend. Bar 25 (pictured) and White trash on the North side of the river, Club de Visionaere, Arena swimming pool and Kiki Blofeld (down an alley way by Tresor) on the South side. Follow the links to find them on the gay berlin map.
Or just take a walk along the North side from Warschauer Str U-bahn down Mühlenstrasse and holzmarkstrasse. You'll see the last big part of the Berlin wall and find some parties on the way.