mars bar is at 2nd ave and 1st st.
there's always parkside lounge (houston and ummm.. something eastish.. around essex). love. get there on the right night and you can score free beers and games of pool from the bored bartenders.
i also really like dempsey's pub (2nd ave and 4th st.) cheap beer, great atmosphere. pool, darts, live irish music tuesday nights. and the bartenders always remember my name (although that may speak more of me than the bar).
and rudy's. (9th ave and like 48th). free, yes, free hotdogs.
if you're in brooklyn:
boat is fun. smith and warren st. they have a dungeons and dragons night.
enid's, too. i used to live right around the corner (manhattan ave. and driggs). hipster scene. go there to be 'cool'.
check out north six, on n. 6th and... something.. kent... or wythe. between them. they are one of the best places to catch bands, and they have great drink specials. show 'em some love.
'contrariwise,' continued tweedledee, 'if it was so, it might be, and if it were so, it would be; but as it isn't, it ain't. that's logic!