John,
I've got the Joe Kane Reference Laser Videodisc from a decade ago that has a full suite of TV test patterns. I select the pattern I want to use or color bars and pause the player. On laser I get 420 lines of horizontal resolution.
I discovered a much more recent offering on DVD that also plays on any computer's CD-ROM drive. At $49.95 it isn't too pricey, that was about half what the Joe Kane disc cost me. I'm not endorsing this product, just happened to find it on a Google search. I wouldn't mind picking one of these up though.
http://www.itworks.com/products/DVDref-suite.htm
There are also free test paterns available on the web and generator programs to work in your computer. Google search term "Test Pattern".