If you're broke but want to eat great, I recommend Bocadillos, which has become a regular stop for me and my friends at least once a week.
The food is truly excellent; the €5 piadina kebab fills you up completely and is a sight to behold.
Unfortunately, I had to give the atmosphere 3 stars because there's not much seating overall and there are only two tables outside, but that's really the only flaw.
It's worth trying at least once in your life because it's truly a guaranteed hit every time we go.