Ignoring the plain decor, Jo-An is one of the best options for cheap japanese food on the Upper West Side. The tempura udon is excellent! They also have great vegearian sushi options, try the AAC (avocado, asparagus and cucumber) roll! I just find myself going back there again and again, and can't figure out why Columbia University people eat at Tomo when Jo-An's is so much better!
Note: for some reason the sushi doesn't seem to be as good on mondays (other days of the week are better!).
Pros: cheap, good japanese food
Cons: plain decor