there isnt much to tell them apart. if they use cherry keys then they will all be pretty similar in quality. buckle spring keyboards are again slightly different but just as good depending on what you use em for... for gaming cherry black and cherry red seem to be the 2 popular choices as 1 gives a tactile feel while the other gives a smooth but firm feel... really its just down to preference. typists prefer the tactile while most gamers prefer the smooth. the other cherry keys give a mixed response when pressed some click, some smooth and click, while others are tactile but dont click.(or at least there quieter)... but again just a preference. when it comes down to it you really do have to nit pick to find the best. things like anti ghosting, buffer size, poll rate or interrupt driven. but none of these features are make or break...
das and cherry company make some of the better known keyboards but there are a good dozen companies that make em, and most of em aint well known to gamers.
the good thing lately is the resurgence of mechanical keyboards by gaming peripherals manufacturers like cyborg, corsair, razer and so on... but many of these are taking a half assed aproach... the corsair for instance has mechanical main keys and dome keys for the macro keys. razer offer a nice product in there black widow but its very much over sized and the poor design of the feet means it can slide around on a polished desk... in other words we seem to be in a feeling out stage, where the makers are coming out with different ideas until they hit upon 1 that people like at a reasonable price...
for gaming grade i would recommend the corsair or razer if you can find them cheap enough but i wouldn't recommend them at there rrp.
i saw a black widow the other day for 66 pounds which is pretty damn good for that keyboard considering its rrp can be 30 quid higher.