I got tired of the mushy feel of the Apple Pro keyboards I've been using, particularly on my G5 workstation at work. I convinced our hardware guy to order a Unicomp USB keyboard for me, with sweet buckling spring love, and so far I'm reasonably happy.
It doesn't feel exactly like a Model M (I know, I have several of those, one in my office for PCs), and it doesn't have the weight (ditto), but it's close enough. First thing I did was use doublecommand to map alt to Command, and vice versa - I can change the keycaps, I suppose, but I don't actually look at the keyboard when I type anyway, which is why I needed to change the mappings.
We'll see how it holds up under extended use, but I feel happier already. The one boourns was it has no onboard USB port, so I had to get another USB extender cable to use with my Mighty Mouse, and now I have an extra cable from the keyboard on my desk. (Apple, why do you ship keyboard extension cables that have notches in them so all you can use in them is your keyboards? A friend suggested it was because they're not rated for USB 2.0, which makes sense, but it's still a pissoff.)
If you like Model M keyboards, but don't want to give up the extra keys on an Apple, I can so far recommend this keyboard.