Yeah I agree with Kath, Sinatra's is one of the first bars you'll come across as you enter the port so definately a great starting point. From there you're only a few steps away from the recently refurbished News Cafe which is always good fun. You cant go wrong with many of the bars in the Port really.
If you're looking for a club you could try Seven on the 2nd line, then on to Icon which is next door to the Puente Romano Hotel on The Golden Mile which is a short taxi ride away.
There's loads of places to go and these are just a selection so it's always worth asking around when you're out where others might be heading.
Hope this helps.