I worked on getting more speed. For me it was because I had no control with the driver and I wanted more distance out of the 3 wood. I got my 3wood swing speed from the upper-90's to the 105-108 range in about month. I used a weighted club device called the swingspeed. I got mine from a buddy but If you google it you'll find info on it.
As Jim said the swingspeedradar (SSR) is a must if you're looking to increase your speed. It'll provide you with real feedback. I loaned my SSR to a local long driver and he was able to pick up a consistent 5mph in less than a week just by experimenting and figuring out what worked for him.
My experience with speed, more is cool but it doesn't necessarily mean you'll play better golf. More distance is good but it also gets you in more trouble - bigger slices and hooks, fatter fat shots, 10-30 more yards right or left on your pulls and pushes, it also makes it a little harder take a little off my shots. The worst part, no matter how hard you work there's always someone faster and longer.