My favorites are Dyad/Aeroheat - they are more round and flatter than the other rims I have built up, making it much easier to build the wheels. Currently running 38-622 tires (Trek T50 tandem). Have Aeroheat rims to build up for project bikes, and will be running tires in the 28 to 40mm range.

Others I have built:
Sun CR18 in ISO590 with 37mm tires; would switch to the Dyad/Aeroheat extrusion in a second if it was offered in 584 or 590 40H.
Alex Adventurer in ISO559 - Surly LHT comes with these rims; I would rank them slightly above the CR18. Using 40mm tires.
Alex R19 (single wall) in ISO630 (actually rebuilt cheapy wheels); surprisingly round and flat; using 28, 32 and 37mm tires.

All of the above, except the R19 are 18mm inside width, which is 19mm.