My own research led me to some wonderfully attractive options like WriteApp for Mac … but a careful look at the Mac App Store reviews revealed that it had been abandoned.
This is truly sad as the marketing on the website will promise you the moon:
Unified Library — No matter where you save your notes — iCloud, Dropbox, Box.net or Google Drive, simply add the location …
Robust Search — The search function in Write allows you to quickly find the note you want by searching through its contents …
But an abandoned app is truly scary. Buyer Beware, I suppose :(