First off, welcome
Secondly, I think the hostel listings you'll find here at TP are quite reliable - so punch in your cities, dates, etc. and see what's available. From there, I would suggest reading the reviews of the hostels that appeal to you on the boards here, at hostelz.com, and bugeurope.com. As a rule of thumb, downplay the reviews that are either TOO glowing or TOO negative, unless you see that they all swing that way for a particular hostel.
Third, in Barcelona - where the language is Catalàn - hostal
means a pension, kind of a low-budget hotel. If that's what you're looking for, cool. If not, be wary that the places with "Hostal" in the name aren't the highly social backpacker havens we know and love
In that case, you want an albergue
, which is the wild and crazy institution we seek...
When's your trip? I'll be at the Home Guesthouse in Barcelona in a couple weeks' time, so I'll be posting a report here.