Rugged Radios are really nice for sure.
For my X I am planning on the same type setup (Ipod - amp - and speakers).
I enjoy fabricating some of my own things as a hobby. I have a few speakers and an amp already waiting to get the X in and start working on my tunes. I am not doing something outrageous or anything just planning on getting some nice sounds while I am out getting dirty!
Speakers - I am using polkdb651's they are rated for marine use and not super expensive. Amp - I got a 4 - channel JBL marine amp. Again nothing super expensive. For mounting and doing the setup I am going to fiberglass my own box mounted to the rear roof (Inside under the roof) and front inside roof. Cant put anything too low because i do get dirty when i go out and play.
I imagine it will take a few trial and error builds to get it the way I want it, but loking forward to this project for sure. I have a buddy with a rzr, he has a marine radio, amp and speakers. The problems he has had with his radio is why i decided to just go the ipod / amp / speaker route.
For an over the counter type setup there are a few that I have seen that do really nice work and quality products. Rugged radios for communicating, J-strong and SSV for tunes, these are the ones I have seen and put out some really nice products. I am sure there are some suporting vendors on the site that may even carry some of the ones here or have solutions of their own they offer. Tunes in the UTV are becomming a pretty big thing, more and more companies are developing good stuff for us to use.