Al Varnell mentions a couple of good alternatives for ASM if you're balking at the upgrade fee for ASM.

X-Assist still seems to work with Snow Leopard. It's a little bit primitive compared to ASM, but the basic functions (i.e. application switcher menu and classic window mode) are there.

Meanwhile, Jack Overfull says that he's working on a new version of multiXFinder (v0.4). At the top of the list is Snow Leopard compatibility. It should be available sometime this month. That's good news for people who like the way that ASM operates, since it's basically the same app.

Personally, I'm debating whether to pay the upgrade fee. I've been an ASM user for several years and had assumed that the upgrades would continue to be free. But, nothing lasts forever, I guess. I'll probably try X-Assist for a while, then multiXFinder when a 10.6-compatible version arrives. If they don't work out, then I can always ante up the dough for ASM again.