Daisy May's has great Texas-style BBQ. The main problem for me is that the location is a bit out of the way (46th St and 11th Ave). To compensate they cater and have a few carts around midtown and one downtown (locations: http://www.daisymaysbbq.com/streetcarts.html)
CATERING: I've used the catering for work meetings a few times and it's always a big hit. The types of things they do well (bbq brisket and chicken, mac-n-cheese) can be done in large quantities.
CARTS: I used to go to the cart on 49th b/w 6th and 7th, but it has either moved to 56th and 6th, or they have added a new one. The menu at the carts is of course limited, but the things I've had have been good and the prices are decent: chili (kind of spicy, $6), brisket sandwich ($7). Also, they sell huge mason jars with sweet, mint tea ($3), which is a nice treat, especially in the hot weather.