Hi Paul,
I'd say look for a leather folio type case. These tend to be bulky but offer the most in terms of (constant) protection. Also look for one that converts to a stand for ease of reading/typing.
If it has a hard back to it then your iPad can double as an in-car entertainment system; by strapping to a headrest. I've done this and it's effective. Not pretty, but effective.
Other options are neoprene covers, but this is only good for protecting the iPad when not in use.
Also, I'd suggest a screen protector for the screen. It stop the screen getting all scratched up, even if it does diminish the clarity a bit.