I'm looking for a hotel in Barcelona during a Holiday in may. Any suggestions?

I'm not looking for luxury or a 5 star hotel, but just a small, cosy and nice place in the center (or close to the center) of Barcelona for me and my wife to stay for 6 nights.

Try gobcn.com. You should find a long list of lodgings of various types.

Or you could go to barcelonaman.com I think there are links to lodging on his website. He checks in here once in a while, and I'm sure you'll find all sorts of good info on his website.

Try this hotel comparison site.

During my last trip I came across a website called

http://hotels.klikgue.com/City/Barcelona.htm

It has quite a large variety of hotels. You might wanna give it a try.

I was just in this wonderful city in January it was amazing...we stayed at Hotel Soho. What a fantastic place. First off you are on a main road so there are tons or restaurants around the hotel, bars, cafes, and shops. The hotel is a 30 second (no joke) walk from two metro stations and bus stops. The hotel its self is very sexy...check it out on trip advisor.
Trip Advisor quotes it a a 230$ nightly average ....you can find it for much cheaper on Expedia.com.
Also you are about a 10 minute walk to the top of the Rambala and 4 blocks or so from two of Guadi's buildings.
Trust me this is an amazing hotel, very sleek, clean, sexy and an AWESOME staff!!