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I have been with Site5 since June of last year and have found them to be very affordable, customer-focused and very responsive to my technical concerns.
One good example of this is that I purchased a Multisite package with them (12 gigs space, 150 Gigs/month transfer for $19.95/month). Well, they began offering a new package with 27 gigs space, 750 Gigs/month transfer for $16.95. I emailed them late Thursday requesting that they upgrade my account. By Friday afteroon, it was changed and I received a credit back on my account.
So, for anyone interested, I can recommend this host. Also, right now, they are offering a SuperHosting extreme package (11 Gigs space, 400 Gigs transfer/month, unlimited DB's, Fantastico, etc) for $7.77/month.
Also, they are the first host I have seen offering Ruby on Rails hosting.
You can compare their plans at:
http://www.site5.com/hosting/comparison.php