Having an online *BSD shell account is great for experimenting with BSD, network debugging or testing environments. There is a number of shell providers available for different flavours of BSD.
If you want to sign up with any do some research with regards to available RAM, speed of the machine, type of processor and server connection speed.
HP Testdrive seems to be one of the better ones, if not the best. If offers plenty of choice with regards to operating systems, have massive servers with plenty of RAM and fast processors.
BSD Talk has a short introduction on free online shells (BSD Talk 8) and a couple of links to providers.
I’d also like to mention the MTV Europe shell project. Though online only part-time and not free for FreeBSD (yet) it comes with a few extras.
I got one server with FreeBSD installed, which is available for access during weekends. If more than 20 people will subscribe I can keep it running 24/7.