When you pick a regulator make sure its a kit like this
NEW CO2 Regulator Solenoid Complete Kit - eBay (item 230308798522 end time Nov-26-08 07:49:57 PST)
Then find yourself a tank (I was lucky to get a free 20lb tank) A lot of gas places will do swap outs kinda like stores do with kegs. But find a cheap tank on ebay dont have to be 20lb but I wouldn't get less then a 10lb tank.
And for a timer for the Co2 I got a timer that I set in minutes instead of 10-15 minute intervals (most digital ones lets you set in minutes) If you cant find a 3 prong timer for it (assuming your regulator has a 3 prong plug) you can get an adapter to put on the timer to make it a 3 prong.
Just make sure you check the Co2 calculator, I set my PPM for about 1500 on the Co2 calculator 1500 seems to be what a lot of people recommend. Also remember to set your fans on a timer to turn off while the Co2 is emitting and sacherating the plants (my fans are off for 20 minutes at a cycle) If I set it longer my temps will get too high so keep that in mind too bro
http://www.hydroponics.net/learn/co2_calculator.asp