I buy mine at a local bookstore. Runners World makes a pretty nice one and it's not that expensive... at least I used to.
I train with a Polar HRM and it logs all my workout metrics including pace/speed, distance, heart rate, and altitude as well as split times (set for miles). These get uploaded via an IR interface to my PC and get stored into an really super calendar that keeps track of time spent in various training zones, mileage, etc. It is hands down one of the best training tools I have ever used. I am kind of an uber geek with toys like this so this is a great motivator for me as well.