I think your photos are pretty good, especially if you haven't done it before.
Your equipment is good, a long lens makes the riders look closer together and that is definitely something the pros do. I personally use a zoom lens (80-200) just to give myself some more flexibility. I think you could add more variety to your photos.
Some things you can try:
*Try some closer shots of just one or two riders faces, don't worry about getting the whole bike in the shot.
*Find a good corner and position yourself so that the riders are coming just about straight towards you.
*Find a good hill on the course, people working hard up the hills can be very dramatic
*Try some panning - move the camera to match the speed of the rider going by, this gives you a moving blurred background with a clear person in front of it. It is a technique that takes some practice.
*Experiment! your camera is digital so you wont' be wasting anything. I usually expect to get only 15 or 20 really good images out of every 150 that I shoot
Feel free to take a look at my photos, I have several gallery's (owner - Eden Palmer) posted here
http://www.nwracereport.com/gallery/
My background is not sports photography, but I am a professional photographer, so if you have any questions about a specific picture I can try to tell you how I did it.