Jeep Wranglers don't have a lot of extra space. That's probably why the hard doors are just designed with door pulls rather than arm rests. I, however, and one of those people who loves armrests in any vehicle I drive. So, I looked for a while until I finally found Misch Armrests. A fantastic product.
One drawback I did have with them is that the passenger side armrest intrudes a bit on the ability for the passenger seat to flip all the way forward with the door closed. This is a bit of a hassle, but well worth it in my opinion.
For about 60 bucks, Misch Armrests are a nice add on to any Jeep with Hard doors.