Eagle Rider was a good deal. Be sure to ask for a discount, they will most likely give one if you ask. They are an Lahania.
Send a message to Hawaiian9'r, he's a great guy and we were able to do some riding together. He'll be able to point you in the right direction.
When we were there we tried to go around the West side of the island which would have been GREAT on a bike but we got rained out. Went through in the Jeep the next day. Road gets a little small (one lane for a while) which would have been easier on a bike. Riding there was AWESOME, even though I rented a gutless Harley that could not keep up with Hawaiian9'r.
The road to Hana is a must. Don't be in a hurry, enjoy the scenery, and I'd go all the way around the volcano. Interesting change in landscape. You have to go to the top of Haleakala as well, watch for ice. When I was there last I rented a bicycle and climbed it. It will be a little faster on a Harley.
Have a great trip, awesome island!