My suggestion is to go for something more versatile than chromakey software if you can. If you're using Photoshop, then a plugin like Topaz Labs Remask 3.2 or OnOne Perfect Mask will both fill the chromakey bill perfectly (both will let you deal with transparency/translucency and small details perfectly) AND will allow you to do extraction/replacement in images that weren't shot on a green or blue screen with only a little more difficulty.

They're not entirely automatic (nor are they free after the trial has elapsed) but with a chromakey image, it only takes a few seconds (with a bit of practice) to do a perfect extraction with the green removed from hair, transparent fabrics, and so on -- and without having to worry about your subject having key-out colours somewhere. I've had little difficulty extracting a subject or subject grouping out of any image using a good masking package (I currently use the Topaz product) unless there's a sort of camouflage effect going on (where everything in the picture is almost the same colour and texture). If you have to spend money on software, it might as well be spent on something that can do more than one trick.