I have the impression Gothic Point Hostel is one of the best. It is well ranked in Lonely Planet and Gomio.com. It is clean, safe (they have cameras all around the place), and economic. Check their web site, you will get a better impression of it.

Hi,

I stayed at the Hostal Opera just off La Ramblas and found it clean, cheap, safe and adequate for what we needed, four females, a weekend away, staying out late. Obviously a great central location and although I know some find it a bit noisy, we certainly had no complaints.

Hope this is of assistance,

Jo