If you are running Mac OS X and doing any kind of development (Ruby, Rails, HTML, CSS, Javascript, C++, whatever) I highly recommend looking into getting TextMate. A friend of mine bought a license as a birthday present for me some number of years ago and I had only used it sporadically. As of late though I have started using it for everything! It is truly fantastic and worth whatever they charge you for it.
My favorite feature? Built in CSS/HTML W3C validation. You would be surprised how many of your CSS bugs that you are quick to blame on browser deficiencies are actually a result of your invalid CSS :/
Posted by Brock 