On your server:
vim /etc/ssh/sshd_config
Make sure allow rsa and the other RSA lines are uncommented
service sshd restart
Make sure the file ~/.ssh/authorized_keys exists(if it doesn't, make that directory and touch that file).
Run this on your client computer:
ssh-keygen -t rsa
(hit enter a bunch of times)
cat ~/.ssh/id_rsa.pub | ssh YOURUSERNAME@YOURDOMAIN.com "cat - >> ~/.ssh/authorized_keys"
Bam! Login without a password!
This is my setup on Fedora VM's running at slicehost.