I love TD games. When its quite at work I tend to play flash based ones on the web. I enjoy most and lets face it, there are some really well polished free games around but I have spent the most time playing the Gemcraft series. Really good gameplay with a lot of complexity as well as a solid RPG system. Every games site offers online saves now which is really handy if I end up on a different PC.
"Always carry a flagon of whiskey in case of snakebite and furthermore always carry a small snake."
-- W. C. Fields