While some mention Rain-X, don't waste your time constantly applying. Pick up some Aquapel and use that instead. A single treatment will last 4-6 months without much breakdown. I recommend ordering it from someone who sells it in bulk, and the applications are $5 or less.

http://www.aquapel.com/

Sales pitch aside (not affiliated with it whatsoever), the stuff works. Make sure your wiper blades are clean as well. Take a damp MF rag and wipe them during a wash. Use isopropyl alcohol to wipe them if the cleaning doesn't seem to help. You won't be able to change the speed of the wipers, but these other steps should help minimize the water clinging to the windshield, and make better use of the wipers during motion.