As far as food goes, just walk up and down Main Street and find what you like.
Sushi? There's more in Greenville than Tokyo. Seriously. Sushi Koji is at the top of Main St and one of my personal favorites. The most popular is probably Tsunami, but it's more to drink at than "known" for their sushi(not that it's bad). My true favorite is Takosushi -- great service, the owner always plays good music, and really unique rolls. They also carry modern-Mexican on the menu, so you can get a couple rolls and a carne asada taco if you like(I do). Murasaki is great too and just a block up from Takosushi. All of these are on Main Street or Tsunami which is a block or so off it.
Barley's was mentioned, and I LOVE some Barleys -- if you like beer, this is your spot. Grab a sampler, which contains 5oz portions of 5 or 6 different tapped beers. Or just browse the list for your favorites. The food is good, great pizza and sandwiches, and the service is solid, a very popular staple in downtown.
One of my favorites is Blue Ridge Brewery -- near the top of Main Street, you can see the copper in the window, and their food is excellent. They make their own ketchup(sweeter than normal) and mustard(stone ground). My favorite sandwich in Greenville is their Cuban. Also incredible calamari with roasted peppers.
I highly recommend the Trappe Door -- it's right next to Barleys, at least, the door is, then you go downstairs....their most popular item is the mussels, which they prepare many different ways, and you get frites with them, and you choose THREE different types of dipping mayonaisses to go with it! I haven't had a dish here I didn't like, their beer selection is excellent, and the atmosphere is creepy cool, I LOVE this place.
Lemongrass is my favorite oriental place, very white-clothy but prices are excellent. The Orient on Main is excellent too, a bargain for the amount of food you get.
Carolina Ale House is MASSIVE and is what it sounds like --- a big place with lots of tvs for sports and solid bar food. Good beer selection.
The Casbah is a top-notch tapas joint with cool art and people, and great food, just tapas style so it's small portions to share with your table.
Rick Erwin's, Nosedive, and Sobe's are my favorites on Main St for the higher priced experiences.