I will second (third? fourth?) the recommendations for PH2. What you get, from memory:
* 3 new base classes: duskblade (yet another fighter-wizard, but this one is actually good), knight (a defensive-oriented tank), and dragon shaman (gains beneficial "auras", sort of like the marshall)
* variant class features for all of the core PH classes plus selected other classes such as swashbuckler, and, uh, some other ones I can't remember
* the variant Druid class feature is worth the price of the book alone, IMHO
* new feats, and they are damn good... some may even appear TOO good, depending upon your tastes; lots of feats to make single-classes fighters better
* a smatternig of new spells, including some very interesting ones that have growing levels of effect depending upon how long you spend casting the spell
* rebuild and retraining rules, so there is an official way for a PC to dump a no-longer-desired feat for a new one, or even change races or classes -- also two sample adventure sites to go with these rules
* Affiliations, a set of rules around groups the PCs can join, then gain actual tangible benefits that are neatly tied into role-playing hooks... there's an example of play that goes with these rules that made me more excited about D&D than I have been in years
* note, the affiliation rules are getting extensive support in the Savage Tide Adventure Path in Dungeon magazine
* quick-build tables for generating N/PCs, with suggested skills, feats, equipment, spells, etc. -- this is also worth its weight in gold
All in all, PH2 is extremely solid.
DMG2 is a fantastic book also, not quite as universally strong as PH2, but plenty good. Ask if you want details.