Amazon has Inception (Three-Disc Blu-ray/DVD Combo + Digital Copy) on sale for only $17.99! If you have prime it will ship for free, or as always any orders over $25 will ship for free.
Some nice blu-ray titles that are still pretty cheap:
Despicable Me (Three-Disc Blu-ray/DVD Combo + Digital Copy) – $21.99
Firefly: The Complete Series [Blu-ray] – $25
Shrek Forever After (Two-Disc Blu-ray/DVD Combo) – $17.99
The Departed [Blu-ray] – $8.99