http://www.faqs.org/rfcs/rfc1918.html
There are three address ranges available for private addresses:
192.168.0.0 to 192.168.255.0 - 256 Class C networks of 2^8 - 2 hosts
172.16.0.0 to 172.31.0.0 - 16 Class B networks of 2^16 - 2 hosts
10.0.0.0 - 1 Class A network of 2^24 - 2 hosts.
Note that the above networks are delineated as they were known pre-CIDR (Classless Inter-Domain Routing). With CIDR, it doesn't matter what your network mask is - you could use all of 192.168.0.0 with a 16bit netmask, if you wanted to, if your routing protocol can operate in a classless manner.
At home, I use 192.168.1.0 for my internal LAN segment, and 10.0.0.0 on the exterior boxes as secondary addresses so I can talk to them without having my conversation "seen" by others on the subnet (at least, not easily). That, and my DSL "modem" has 10.0.0.1 as a management IP, so I can access it without extra hardware.