In reply to peaterpan:
Why are you looking to get helium cams? They aren't very good.
Dragon/Camalots are much better.
Joe Brown do a great deal on Dragons where you can get 4 for £160, £40 each.
If I was starting out and getting 4 cams to begin with. I would probably get purple, green, red and yellow if I climbed in the Lakes/North Wales. If I climbed on granite or gritstone a lot I would get green, red, yellow and blue. And if I climbed on limestone a lot I would get grey, purple, green and red.
If you are on a supertight budget. I'd probably get DMM 4cus which can be had for £30 each. They aren't as good as Dragons or Camalots, but they still work.
I'd probably get sizes 0.5, 1.5, 2.5 and 3.5.
HTH Tom