I've been meaning to write about Rails Playground for a while. I currently use their level 2 developer hosting and I've been very happy with it. I host several domains and subdomains on my account. I run several rails apps (including my online wedding registry site, this blog (WordPress) and a wiki (moin) on it.
You get shell access, sFTP and cPanel, MySQL, PostgreSQL and also unlimited subversion repositories. Another neat feature is that you get 2 mongrel instances included. You need to ask Rails Playground staff to set these up for you, but they are quite prompt and friendly. I did have some problems with Mongrel instances dying, but the Rails Playground staff added a cron job to restart them, and this has solved the issue. At currently $12/month (or $9/month if you pay for a year), it is quite economical hosting.
I'd highly recommend Rails Playground if you're a rails developer looking for hosting (with fcgi and mongrels) and subversion, and you don't want/need the flexibility/hassle/higher price of a virtual private server.