There is one place in Little Italy that's terrific - Luna's. It's a hole in the wall little family run place - unlike the fancy-dancy Ital-merican places all around Little Italy.
Find Luna's - you will not be disappointed.
For some good Tex-Mex, there's Tennessee Mountain in SoJo. Terrific Nachos.
For a Themed place, try one of these two places:
Jekyll and Hyde's (There are two locations, I think) Here's their website:
http://www.jekyllpub.com/ Fun place, good food.
Mars 2112:
http://www.mars2112.com/ Very kid oriented, but still a fun place to go.
If you're around the theature district, and you're into a casual european type place, then check out Cafe Un Deux Trios:
http://www.cafeundeuxtrois.biz/pages/831018/index.htm
Have fun!
-Zoltan.