Thanks to abjr (again!) for sending me links to new providers. RapidXen is offering cheap Xen VPS plans in either Chicago or Fremont (although at this point of time, Fremont CA is not available). For $5/month you can get a low end VPS wit the following spec:
64MB memory
256MB virtual memory (swap?)
5GB storage
Debian, Ubuntu, Fedora, CentOS, [...]