I have an external drive that was dropped. It doesn't mount anymore on my OS X box and Disk Utility doesn't see it. Is this the point where I'd need to bring it somewhere for expensive data recover?
Yep, if the platters were spinning when it was dropped, the heads may have crashed and recovery may be impossible. If the drive was powered down, it's more likely that a wire or solder joint (or circuit board) is broken.
It could be a cheap five minute fix, or a "throw it out and get a new one". Either way, someone will have to crack the case and take a look.