Off the top of my head, I would recommend (not necessarily in this order)
Hampton Street Vineyard
Any particular vibe or type of food? BBQ? Cafe? College crowd? Upscale? Southern homestyle?
Hampton Street Vineyard
1207 Hampton St, Columbia, SC 29201
Pawley's Front Porch has outstanding Burgers/Sandwiches located in 5 Points. Taqueria Jalisco Mexican Restaurant is a good Mexican place.
Pawley's Front Porch @ 827 Harden St., Columbia, SC 803 - 771 - 8001.
Taqueria Jalisco Mexican Restaurant @ 612 Saint Andrews Road, Columbia, SC 803 - 731 - 5546.
Taqueria Jalisco Mexican Restaurant
612 Saint Andrews Rd, Columbia, SC 29210
I'm guessing John must've stayed at one of the hotels on Main St., and only ventured a few blocks in any direction; that would discourage me, too. However, if you're willing to expand your hunting grounds to cover Downtown, the Vista, and Five Points, Columbia has a lot of options, actually.
I'll second the aforementioned Terra, and Motor Supply Co., and add Mr. Friendly's. All three of these have pleasantly eclectic menus and great service. For a tapas-and-wine approach, you have Cellar on Greene and Gervais & Vine. There's excellent upscale (but not pretentious) Thai at Baan Sawaan (also, their beer menu reads like one of the old J. Petermann catalogs; it's quite clever).
If you're into oysters, the not-so-cleverly named Oyster Bar has good ones, and they shuck for you as you're eating. The Flying Saucer is part of a chain, but the food's quite good and the beer selection is outstanding. Likewise, the Hunter-Gatherer Brewery and Alehouse a few blocks away makes excellent beer and terrific entrees to pair with it (I'm especially fond of the Caw Caw Creek Bratwurst there; the pigs are raised and the sausage made locally).
Then there are the downtown Miyo's restaurants: Miyo's, M Vista, and M Cafe. All serve fresh, healthy, delicious pan-Asian fare. I live northeast of town, and was thrilled when she opened one near me.
The more I write, the more I keep thinking of. If you mention what part of town you're staying in, and what kind of food you really go for, I'll try to be more focused.
931 Senate St, Columbia, SC 29201
100 State St, West Columbia, SC 29169
701 Lady St, Columbia, SC 29201
Gervais & Vine
620 Gervais St, Columbia, SC 29201
Hampton Street Vineyard (great food, but it can be pretty dead at night - awesome at lunch)
M. Vista (should be your first stop if you like Asian food)
Restaurante Divino (excellent Italian food in a special occasion atmosphere)
Terra (really excellent food from a chef who spent time in one of Frank Stitt's kitchens, but who sometimes misses on a dish here and there)
Motor Supply (semi-creative menu and good, but not great food in a great atmosphere)
Gervais and Vine (small plate menu with an excellent wine selection and a sophisticated atmosphere)
Baan Sawaan (really excellent Thai in an intimate setting, a bit pricey but worth it)
GREAT PUB GRUB:
Flying Saucer (enormous beer garden with really great beer-friendly food and waitresses that I like to admire)
Hunter-Gatherer (a U of South Carolina institution, and a great pub atmosphere)
Pawley's Front Porch (good, creative burgers sometimes served on stale buns; burgers are definitely not great, and the menu options beyond burgers are very limited. a lot of people enjoy it, though)
MORE SOLID CHOICES FOR COLUMBIA:
Mucho Margarita (in Five Points, next door to the overrated Pawley's Front Porch. Kind of a dive bar sort of place, but they have the best and most authentic Mexican food in the Midlands of South Carolina. An undiscovered gem)
Mojito's Tropical Cafe (really excellent Cuban food in the Vista area, half a block from the State House on Gervais Street)
819 Harden St, Columbia, SC 29205