One of my favorite is 18th St. Bar and Grill: all-day happy hour! $4 well drinks (and Heidi pours a strong drink) and $3 16 oz. draft beers
Hungry Hunter also has a good one: half price on most of their appetizers, well drinks, and house wines. 2-6 m-f if I remember correctly, but also all day when the game is on (football I think and it might just be Sunday)