1. add more RAM (2GB should be ~$5/month)
2. since you are not attached to Apache (wpmu), try installing nginx (or even lighttpd) and quit using shitty php modules.
3. delete all the plugins you are not using and reconsider deleting some of those you are, but don't necessarily need them.
4. then install some wordpress caching add-on - in this case check out:
http://wordpress.org/extend/plugins/...he-integrator/
5. say thank you! - your system will decrease cpu load significantly.