Nightfall
Sage of the Scarred Lands
Psion said:Aerth.
Don't have that one yet, but it has the virtue of being fairly self contained, and it steps right into tons of adventure support (being the backdrop for all of Goodman's DCC adventures.) And it's pretty fresh.
I like it also because it offers a way to do an Adventure path for players that doesn't necessarily require you to use the Box Set too.
Not that there's anything wrong with a box set.