My laptop! I've found more great deals from various deal alert boards online, not to mention the various coupons and boards with good ideas.

My bread machine - it has saved me a lot of money on bread and it tastes so much better and I know what is in it.

little calculator in my purse - I often use it to check out what is actually a better deal - figure out the price by the oz - sometimes big is better and sometimes not.

freezer

I have all three copies of the Tightwad Gazette books. I know a lot of the ideas are non-conventional, but I read them mostly for inspiration. They kind of just get me fired up to use less and save more.