Amana also has an ultra-cool slot cutting bit. It's like a
dial-a-dado, but it's a router bit. You loosen a nut and turn a knob
allowing you to adjust the cutter thickness. It's not a rail & style
set but you could probably recreate the same profile with normal bits.
It's about $100 iirc, but I think it's worth it to get an exact fit and
be able to use it for everything from 1/8 to 1/2.

brian