Anyone have any tips on buying a used fridge for making lagers? Size, models, things to keep in mind?

I guess that really depends on your other equipment, and how much you're brewing/planning to brew.

For only 1- 5 gallon carboy, you can use one of those small GE fridges (think kegerator fridge) with just a little bit of modification.
For 2 or 3 - 5 gallon carboys, I'd prolly use a chest freezer. No modification necessary, if you buy the right size.
I've seen pics of stand-up freezers modified to hold 3 fermenting carboys, and even a keg or two.
For a large assortment of kegs and carboys, I'd look at one of those very large chest freezers. You can prolly find some older models for relatively cheap.

It all amounts to how much you want to brew. If you think you'll be content brewing 5 gallons at a time, stick with something small. If you think you're going to be doing a lot of brewing a little ways down the road, get something that will accommodate a few extra carboys. If you've got kegs, and intend to brew a lot, go for the larger models, and it can serve double duty as a kegerator with lots of taps.

That's my $.02 anyway.

Cheers,
Dave

Thanks. I found a normal fridge/freezer on craigslist for $25, so that made the decision for me.