While helping out a colleague with a research effort to help find the right GUI testing tool I came across this article. I think it does a pretty good job laying out the different kinds of testing and references some good open source tools that you could use. It of course mentions the big players, Rational Functional Tester and Eclipse Test and Performance Tools Platform (TPTP).
If you are still doing manual UI testing then you really need to evaluate your resources and the cost to your software company when bugs are found on the shipping product.
You simply can not afford to not use automation.