What is a good ratio of developers to testers?

Joel makes a good argument for 1 tester for every 2 engineers, as well as covering the excuses people use for not having those testers.

I blogged about this once here. The most relevant excerpt is below.

"I've seen high quality products produced on a 10:1 dev:test ratio, and horrible products created with a 1:1 ratio. The difference is in attention and care for quality. If everyone (including management) on the team deeply cares about the product quality, it has a good chance of happening regardless of the ratio. But if quality is something that is supposed to be tested into the product, by all means have at least 1 tester for every developer - more if you can get them."

There was a recent, relevant article on InfoQ that you might find interesting.