There is no whitewater rafting on Roatan but there is on the mainland. You would take the ferry to La Cieba and I would recommend Omega Tours (http://www.omegatours.info/). They should pick you up in La Cieba and bring you to their location.
Usually the cost for the rafting includes a nights stay so you may want to consider that as well. Water volume fluxuates which increases/decreases the difficulty level.
It is a fun trip and while exciting I wouldn't fret over it too much.
I would take dramamine for the ferry ride both ways. When you buy your ticket ask them for some and they will give it to you.
Dan

All good advice above - if the tickets sellers don't speak English just ask, "Dramamina?" and they'll ask you for a number - you want 2 each if you tend to get sea sick and take them at least a half hour before you set out.

We're experienced rafters (have our own set up we use on the Deschutes River in Oregon in the summers) and found the equipment and guides at Omega to be really great. If the guides know you're new to rafting and nervous, they'll really work with you on everything you need to know. There are various places along the river they can choose, too, to affect the difficulty. The stretch we did was pretty wild with lots of water following weeks of rain; not for the faint of heart. You might want to contact them ahead and get their opinions about your options - nice people. Check out the Honduras 2006 collection below - travelogue link is on the main page. Good luck!

We also went white water rafting at Omega Lodge. We were a mixed group.. some experienced and some not.. They made sure that the beginners had a guide that would be able to take care of them. We had a great time. Our trip wasn't as wild as Hopeful's.. thank goodness..
Oh, and dramamine or not.. I got sick on the ferry both trips to Honduras. Enjoy

Sorry to hijack your thread, lojoblais, but I have a question for those who have been on the ferry. I've read a lot about people getting sick on it. Are the seas really rough between Roatan and the mainland? Or is it the length of the trip that makes so many get sick, or the type of boat?

The new boat to Roatán is nice but on a rough day I can get sick about anywhere. Crossings are often easier in the mornings. Have you tried Sea Bands? They are accupressure wristbands and, as skeptical as I was originally, I swear by them now. I have them out and ready to help with nausea after my shoulder surgery on Tuesday.

http://www.amazon.com/Sea-Band-Original-Wristband-Adult-Size/dp/B000GCMXZM

Here's another kind I'm going to give a try on an upcoming road trip:
http://www.amazon.com/Psi-Bands-Drug-Free-Relief-Nausea/product-reviews/B000XB9GKG/ref=dp_top_cm_cr_acr_txt?ie=UTF8&showViewpoints=1

Happy trails!

Thanks for the advice & yes, it's good to know about the sea crossing because that would definitely affect our decision as to whether or not to go. And I will certainly try the Sea Bands.

I usually don't have a problem with sea sickness, and I've been on a fair share of boats. But there is always a first time...and this crossing sounds like it has affected plenty. I may take the dramamine just in case!

The last time I took the ferry from Roatan to Le Ceiba and back was the LAST time I will take the ferry! It is a relatively new and modern boat. The trip to La Ceiba not to bad. The afternoon return to Roatan they handed everyone a barf bag and paper-towel. Oh my gosh! Everyone on board (excluding crew, and for some unknown reason, my husband) was very very sick. I truly wanted to die. There are some crossing currents that on a windy day bash you around. The crew know what to do to get the boat to port but...there is a good reason for the ferry being knick-named "the vomit comet." I personally will only ever fly from now on. There are numerous flights to the mainland from Roatan every day. The cost is about double the ferry, but in my opinion worth it!

As for the original question. There definitely no rafting on Roatan, but lots else to do