One of the things I love about Charleston is that this town loves its happy hours! The best place to find out about happy hours is through dish, the printed mag of the Charleston City Paper, or you can just check it out online here...http://www.charlestoncitypaper.com/
WOK has mediocre food but a pretty great happy hour drink special, SOCIAL has great food and drink specials, and McCrady's has a fantastic bar snack menu available.
2 Unity Alley, Charleston, SC 29401
The best happy hour I have found has been Charleston Beerworks. The place itself is nothing great, but most of their (rather varied) selection of beers is $2, and high gravity are $3, or so, before taxes (also their Sam Adams is $2.50 outside of Happy Hour). They have 2-for-1 appetizers, and while their food is nothing great, it includes wings, so you can get 12 somewhat decent wings at about $5.65. The wings at Moe's are also half-priced during Happy Hour, but I didn't think they were great. The food at O'Malley's and Midtown is terrible, but O'Malley's has half-priced draght beer, though limited offerings. Chai's has a discount food menu at Happy Hour, which means it is correctly priced, Social has a $3 food menu, and their $3 beers (half-priced) I don't even think come to 16 ounces. Finally, Mellow Mushroom has a wide variety of craft beers that are half-priced from 4-7, which comes out at $2.50-$3.00 before taxes. Other than that most of the places seem to offer only a dollar or so off, from what I have found. Usually, I go to Beerworks.
King St. Grill has $1 off beer and $2 off liquor from 4/7 on Saturdays. Mad River Bar and Grill has Saturday Specials from 5/8 offering $2 draft beer, 1/2 off martini's, $1 off liquor and 1/2 price appetizers.
King St. Grille @ 304 King St., Charleston, SC. 843 - 723 - 5464.
Mad River Bar and Grill @ 32 North Market Street, Charleston, SC 843 - 723 - 0032.