I like slider even though I don't use it all that often. While the sliding and the fading in/out effects are great, it takes a brief moment to complete. Not for the excessive optimizers.
A couple of things to note though. It doesn't play nice with Growl. It slides in the notifications nicely, but it flickers back into place slightly on the exit. Nothing harmful, just odd. Same sort of thing with InvisRay, except on the start. It flickers for a moment as it begins the display. Again, purely cosmetic, but worth noting. If you use Unsanity's APE you might as well try it out.