Alot of places are more inclined towards serving food/beer rather than just being/bars/clubs.
That said there's still plenty around Wenceslas Square and near where the market is held, try and find the tavern/cellar type bars as these tend to be the best ones for beer/ crowd/ atmosphere/ prices.
Captain Nemos is a good club but it's very hot inside so the ladies tend not to wear much
BEWARE PICKPOCKETS !
The public transport is full of them and the main tourist areas too.
They tend to follow you until you stop to cross a road at traffic lights or pedestrian crossing then 'dip' you.
There are more through the day as they tend to get the cash then buy a 'fix' & so are spaced out by night.
We saw loads of them operating and were followed on a few occasions.
Avoid taxi drivers wanting to take you to gentlemans clubs too.
You'll get taken to a seedy bar on the outskirts of town, ripped off and lucky to get back with any money left.
That said if you keep on your toes you can still have a good time and a laugh with the lads.
Try the bratwurst sausage that's for sale from the small stalls in the square on an evening too,