I think that Into the Breeding Pits is worthwhile (not that it's expensive to begin with). It's not totally revolutionary, but it has some rules for dungeons, such as modifications to certain spells (height limits, not ending up in "dead space," visibility range, traps, etc.).
There is a new monster encounter chart, which is less undead heavy, and introduces new monsters such as gnolls (obviously), hydras, minotaurs, etc. The gnolls are cooler than the cultists from Thaw of the Lich Lord since they are equivalent to the soldiers you can hire (i.e. thugs, knights, barbarians, etc.).
There are new items, obviously. Since I love the D&D cleric class, I'm rolling with a Thaumaturge, and was thrilled to see the Armor of Righteousness. It is for the Thaumaturge only, and confers +2 Armor, but prevents the wizard from casting spells from the Necromancy, Summoner, and Elementalist schools of magic (ouch!).
There are also rules for the Beastcrafter, which is analogous to the Lich in that you gain new abilities and such. There are three levels of improvement, with the wizard becoming more animal like with each stage. You can even gain bestial enhancements, such as claws and even wings.