Long time resident of the area, so believe me when I tell you to avoid the Campus Inn or Bell Tower. They sort of have a lock on university visitors since they are the only ones downtown, but lots of bad reports lead me to never ever book anyone there unless they have no transportation. If you have a car, stay out on Green and Plymouth Rds (north campus) or Boardwalk (south of town near I94) just a five or ten minute drive downtown.
The Ark is one of the gems of Ann Arbor. Depending on the popularity of the act, they sometimes sell reserved seats at $5 more a ticket. Otherwise it is general admission and the fans line up on Main street anywhere from 7pm on. Usually doors at 7:30, show at 8. There is not a bad seat in the house however. You can buy liquor there only if you have a membership, but they do sell one night memberships. Otherwise they have teas, and soft drinks, Zingerman's baked goods, and such for purchase.
All the restaurants on Main Street are very popular, so allow at least an hour and a half to get dinner. Real Seafood is a standard crowd pleaser, or Gratzi for Italian. My personal favorite is the West End Grill around the block from the Ark on Liberty. You MUST have reservations though to make sure you get in, it is small and popular. The meals are from $20-35 but you will not be disappointed. We particularly enjoy the bartender's martinis and cosmos, very generous and tasty. Other standouts are Shalimar (indian), the Earle or Cafe Zola. Watch out for the bar/pub scene, (i.e. Old Town, Conor O'Neils, Full Moon) if you are young and only care about drinking-- lots of fun, but the food is sub-par (actually I wanted to use a word for what the vacuum does but the site wouldn't let me - ah censorship). If your budget is limited try Grizzly Peak, a brew pub on Washington, two blocks from the Ark.
After the Ark, try Sweetwaters on Washington and Ashley for coffee and dessert. Or go across the street from the Ark to Improv Inferno, $5 cover and lots of crazy laughs.
Don't forget to take a stroll through campus while you're here, and if the weather's good a trip to the Arb is not to be missed.