I recently moved from b2evolution where I had a cool piece of code that allowed me to select multiple categories as a search. It was called Before & After Categories Plugin (if I remember right, it was written after I requested it) and it worked like a charm--it generated selection boxes before each category and radio buttons for ANY, ANY BUT, and ALL.
WordPress has a much better search feature, but I'd still like to have the multiple category selector as I often want to search for a group of posts that wouldn't come up with a search. (For example, if I type "firsts and owen" in the search box, I get a result of one post. But I know there are at least 25 posts that are tagged with both the Firsts and Owen categories.)
I've looked at all the category selector plugins but haven't found anything that gives the result I'd like. Is there one I'm missing? Is this something that can easily be written?
Here's a sample photo (from the Wayback Machine) since I obviously no longer have that blog setup (it's moved here).