Castle Whiterock is the best 3rd edition boxed set, imho.
The 51.5 prequel is excellent too.
Some other gems you may want to try and get your hands on before they are gone...
#7 The Secret of Smuggler's Cove
#13 Crypt of the Devil Lich (very ToH like)
#16 Curse of the Emerald Cobra
#26 The Scaly God
#28 Into the Wilds (I love this one, reminds me of B2 from the basic set)
#40 The Devil in the Mists (a good sequel to #7)
#44 Dreaming Caverns of the Duergar (probably the best "underdark adventure" for lvls 1-3)
Those are some of my favorites from the 26 DCCs that I've picked up this year. I also managed to snag the super rare #35 from one of the nicest people on the RPG industry. I was late to try Goodman's DCCs but if GG ever makes more 3.5 stuff, I'll be all over it.