I bought two Calumet light stands, they weren't cheap at about £40 each but they're really good quality and are air sprung - this is desirable as you don't want your nice but delicate flash crashing down when you undo the screws...
You will also need a flash/umbrella adaptor which are usually about £18 ish (you can buy cheaper online). There are two types, one with a cold shoe on the top and one with a screw thread on top (this being a brass spigot with a 1/4 thread on one end and a 3/8 thread the other) for simplicity you really want the cold shoe type. The umbrella shaft goes through a hole in the centre and another threaded knob keeps it in place. Make sure you have the umbrella going through the right way round. All light stands are basically the same design but some are better than others. I like the Calumet ones because they are very sturdy and also quite light weight.
If you head over to the Strobist blog (first result on google for "strobist") and look at his Strobist 101 series he goes through all this in a clear and concise way, and even posts pictures so you can see what you need.