It's come up before in the forums, but never really been resolved: advanced search.
I'm working on updating our own site to support the following:
Advanced Search by:
category
min price
max price
custom attributes
For now, we're likely going to have to cop-out and just do a text search within the product names instead of searching the actual custom attributes (since we can't upload those yet through CSV).
I'm trying to pick my way through the dense and complicated mess of SQL queries in shop.browse, to support the additional features we need.
If anybody has any modules that will do this already, or any ideas on how to simplify this process, please let me know!
And if we get no help and find nothing, I will post whatever I can cobble together up here so everyone can use it. Unless I give up before reaching the finish.

(For what it's worth, we'd probably be willing to pay as much as $200 for a really slick solution, here. If somebody wants to work up a quick advanced search module and make it available to everyone, let me know.)