Okay, you will obviously need more than this list if your doing a pneumatics set up, but I dont fully undertand all the components needed so Ill just give the basics...

Radio Gear (transmitter and receiver) - most people use the Futaba controllers you can get from Technobots but you can get alternatives such as wheel controllers if you like
Materials of some sort - you can pick up some polycarb from Technobots, otherwise I cant help much with metals
Wheels - anything will do, but the RoboChallenge blue wheels are very good and screw right onto the drill thread with ease
Motors (prferably drill motors) - you can get cordless drill motors from any DIY shop or GimsonRobotics sell some ready prepared ones if you dont want to spend hours dismantling and preparing them
Wire - from Technobots, make sure you dont get the really thin stuff though
Crimps (or connector blocks if you cant afford them) these just connect your wires, pretty cheap from Technobots
Batteries - depends on your budget, SLA if you have weight room and a limited budget but NiCad/NiMH if your going for smaller, lightweight but more pricey alternatives, from Technobots
Speed controller (Electronize, IBC, SideWinder) - depends on your price range, Electronize are very basic, cheap and available in the UK while IBC are Australian and SideWinder are American if you want to import (these 2 are also much more expensive but have by far better features)
Cooling fan (optional) - just in case, I just blow a fan onto my IBC so that the fets dont burn out, they are pretty cheap and its better to be safe than sorry... fans are certainly cheaper than speedo repairs

Thats all I can think of at the moment. For your flipper you will want some rams, a canister and stuff like that which add to the weight and price. I have no experience in pneumatics so its better to ask elsewhere.