You don't mention how much your budget is, but if it's around £400 for a gun, simon's suggested guns are both perfect. You will need a scope that will add about £50 you can probably fill up each time you visit a club for about 50p a time. Alternatively you can look at CO2 powered guns which are cheaper to buy. You will have a choice but obviously smaller and lighter, something like a crossman ratcatcher for around £120, no scope required. The co2 bulbs bought in bulk are easy to replace and won't require the upfront investment of an air bottle or pump.
Hope this helps
EV2 mk2 with 2009 big Nikko
HW97K with 6-24 Nikko Nighteater