Watir is my automation tool of choice. Watir is free and runs on the Big 3 ~ [ Safari, Firefox, IE ] Watir combined with Cucumber and its /Regular Expression/ capabilities, allows the very readable and maintainable scripts. This combination allows me to sit with Management, Developers and most importantly Clients to create or easily portray my automation work. I've started my own Testing Framework, Watircuke, that appears to be gaining traction in the community.
I also enjoy getting "close to the metal" with RSpec.