iphone notes app that supports Dropbox sync, search, import text files automatically
I currently use Simplenote to sync with my nvAlt on my Mac. While Simplenote is doing the syncing, you can configure SimpleNote to also sync to Dropbox, or you can have nvAlt store the files in Dropbox on you Mac.

A little more in line with your question, I have used Notesy in the past. It uses Dropbox for syncing, and nvAlt could still access the files via Dropbox on my Mac. However, It was very slow to search, and I recall it had several other annoyances. I haven't tried recent versions, so it might be better.