PuffTheMagicDragon, we stayed just off the Rambla which is sort of the main street through Barcelona, so very central. Wouldn't reccomend our hotel as it was a flea pit!!!
DH is saying that when he went with a work collegaue she took him to the Basque quarter (that's the northern spanish bit not the underwear bit - or should I say it better not have been .
Would definitely recommend that you take a tour on the open top tourist bus, sounds corney but it gives you a great insight into the city. You can jump on and off as you wish and they also give you a good book of discount vouchers for most of the best attractions, so best to do this first
Good places we went to include Parc Guell, Casa Mila, Sagrada Familia.
If you are looking for nightlife you could go to Port Vell which is at the end of the Rambla, but we found it really expensive and as we're not really a clubbing couple we just went and people watched but drinks were a lot more expensive here than in the little tapas bars etc.
We recently stayed at the Hotel Apsis Atrium which was lovely. Superb hotel, great location, close to everything and very reasonably priced (had a pool, sauna, hot tub etc). It was just down from Placa Cataluyna - maybe a 3 minute walk. We didn't do clubbing etc but we did find some nice tapas/wine bars to drink in till the wee hours of the morning. Was great fun and we can't wait to go back again. We went to a restaurant on the Ramblas called Attic which was really nice. Good wine, nice food. Agree that the tourist bus is a must.
I would recommend staying somewhere close to las ramblas if you're only there for a couple of days - in the barrio gotic which is the old town and very pretty. There's an area to the west of the ramblas called the raval (iirc) that is seedy. The north end of the ramblas is less seedy than the south end.
There are some GREAT tapas bars on the Passeig de Gracia (short walk north of placa de catalunya) - Bar Bar Reeba was one of our fav haunts. Avoid eateries on the ramblas - overpriced and not very good!