Automated Testing using Selenium

For browser-based testing of web applications I recommend Selenium. It can be used both for functional, compatibility (it has extensive cross-browser support) and regression testing.
I used the Java Api, but it is available in other languages.
There are other tools similar to Selenium.
In my team we use it and we feel quite comfortable but for a brand new project I would rather review some other tool. Anyway Selenium is great.