I'm a big fan of AppRocket. I love the way it flattens my hierarchical file system and makes all files under its purview available within just a few keystrokes. I find it especially useful for any large music collection.
My gripe with it is... it too is a memory pig. I've maybe indexed 7500 files and to do what app rocket does - it takes up a colossal 20 megs. 2k per file. Crazy. Since it runs in .net, I'm sure it was written in C# and dines away at the memory buffet like a long lost member of the Donner party. :-<
Of course, it doesn't help that its been completely abandoned.
Launchy isn't ready for prime time yet.