With lump I use Royal Oak from Walmart, BUT, any lump you use check to make sure it is from the USA, the others can have chemicals and soft woods that burn up too quickly. Go to BBQbrethren.com and dig around for threads on it, there are links (or just do a google search) that have detailed breakdowns on size through out the bag and burn temps as well as how long they burn. Getting good lump is pertinent to good consistent burn times/temps. FWIW I use a mix of approx half and half lump and Kingsford briquetes.
Also, once most meat reaches 160 it no longer accepts smoke so keep it down for the first hour or two to absorb the smoke flavor, then do whatever you like to do from there.
Here's a comparison site.
http://www.nakedwhiz.com/lumpindexpage.htm?bag