Online Registration Companies:

Active.com
- Registration
- Active Donation/Fundraising with Registration
- Volunteer Module
- Social networking
- Limited Email distribution to participants
http://www.active.com/

imAthlete.com
- Registration
- Donation/Fundraising integrated with Registration
- Volunteer Module (limited)
- Social networking
- Email distribution to participants
http://www.imathlete.com/

RaceIt
- Registration
- Donation/Fundraising integrated with Registration
- Volunteer Module
- Social networking
- Email distribution to participants
https://www.raceit.com/

Others:
Kimba: www.kimbia.com
Race 360: http://www.race360.com/?c=lt
Race Nation: http://racenation.com
Races Online: http://www.racesonline.com/
Run SignUp: https://www.runsignup.com/