For barbeque chicken, pulled pork, or ribs, my local place is Kloby's Smokehouse in Laurel. This is Johns Hopkins Road where Laurel, Fulton and Columbia come together. Very convenient off Rte 29. You order at the counter. You take away or sit at the casual tables. Folks in the comments also mention Bare Bones and Pig Pickers, both on Rte 40 in Ellicott City.
For pit beef and other barbeque, some people really like Canopy on Rte 40 in Ellicott City. I enjoyed Uncle Grubes off U.S. 1 in Elkridge. Nice beef with a charred edge, served with surprisingly good coleslaw. You order at a counter and can eat outside. Definitely check to see if they're open in the winter. I called, but got a busy signal. (In the Kloby's post, I linked to some Chowhound posts about pit beef.)