Jacks is great on week nights, never been on a Saturday. It's on Isabella Street and is often packed (in the week) so reserve some space. Depends what sort of night out you want really, and how close to Waterloo. If you want to be close to the station there's not much choice, could try The Stage Door, tucked behind the Old Vic or there's a latino type bar on the corner of lower marsh (but haven't been there in yonks so no idea what it's like now.) or the Fire Station but you need to be the kind of person that likes that kind of place or you'll hate it. Like Marmite.