Delphinia picta. A type of picture-winged fly (family Ulidiidae), 7 mm long. I had absolutely no clue what this was (other than some sort of fly). And a text search on likely keywords didn't get me anywhere. I finally ID'ed it by sitting on the BugGuide.net main page for Diptera and hitting 'refresh' until one of the random thumbnails popped up with something vaguely similar, then 'walking the tree' from there -- went up to the superfamily containing the hit, clicked on the Images tab, and paged through thumbnails until I saw my guy. Will have to remember that trick. Maybe it will work on some of the many spiders I have yet to ID.