Twist on Sheffield in Wrigleyville is a great little place for tapas. It's very small, so it can get crowded quickly. They do have some outdoor seating, but the restaurant is very close to the el, so I'm not sure how quiet it would be to dine outside.
The tapas menu is extensive and delicious, but they do not have the flair that a few of the other Chicago tapas restaurants have. The sangria is good! I would suggest it more for the experienced tapas diner than a first-timer, just because it can be so overwhelming in such a small restaurant.