There's a decent gay gogo/cabaret club one subway stop from the Charles Bridge area. Go to the subway stop nearest the Charles bridge called Staroměstská and go to the Mustek stop. Then walk down Vodickova to Jame street to the Escape Club. Go to the door and ring the bell. They'll buzz you in.
Can't say it's the best club in the world, but it might be the best in Prague. You'll be greeted by some nice looking boys. Don't be afraid to tell them what type of guy turns you on so you don't waste time or money on someone that doesn't do it for you. Yes, they expect you to "buy me drink".
It gets started late, so don't go too early. Full body shows start at 11pm. Drinks aren't cheap, about 80 crowns each, it adds up quick so go prepared. Plus there's a 200 crown cover.
Definitely get the unlimited travel card. It's 110 crowns (about $6.50) and lets you travel any subway or trolley line for 24 hours. It's even cheaper if you get a 3 day card.
It's probably a little cheesy, but go to the top of the clock tower in the old town square and plan on being there at the top of the hour when the trumpeteer comes out to play a little tune. Plus the view is unbeatable.
There's a pretty decent sports bar on Liliova street called O'Che's that has good cheap beer and an utterly adorable bartender that I couldn't stop staring at.
Have fun. Prague is one of the most beautiful cities I've ever visited.