No C-17's at DM yet, although as Tashengurt alluded to, the Boeing YC-14A is there...
Pima Air Museum, just over the road from The Boneyard, is always worth a visit if one's in that neck of the woods. The '14 was there a few years back. Recommend the Titan Missile Museum too, a short (by US standards) drive South of Phoenix (and even shorter from Tucson).