We've used dream host for roughly 5 years now. I dont have any complaints. We had some slow load times the first few years, but that was likely to the joomla install we were running. They certainly make it easy to get up and running and lots of options for growth.
If you're a non-proffit organization they will host and provide domain name registration for free. I can attest to that.
Specifics are here:
http://wiki.dreamhost.com/Non-profit_Discount
Its hard to beat free. And any time we had a server sideissues that we couldn't resolve ourselves, they've been quick to respond.
If you're affiliated with a public school, the school likely has 501c3 paperwork. See if you can get a copy to forward on to DH and you'll be all set.