I spend a fair bit of time surfing the Web (like that's news). As a result, I come across a lot of stuff that I'll eventually use in class. One of the reasons I started this blog was to have a place to keep track of all those things.
Matt Evans (a financial consultant located in Arlington, VA) has put together a truly impressive colletion of spreadsheet models. A lot of them are valuation based (i.e. models for valuing a firm based on Free Cash Flow, valuation of Synergy in a merger, etc...). However, he's also got a good assortment on other topics, like valuing options using Black-Scholes, lease-vs-buy analysis, and others. If you're a finance prof (or student), check them out - you'll almost certainly find something you can use.
HT: Jim Mahar at Financeprofessor.com