If you refer to the IP Address of your current computer, you're looking for ifconfig and iwconfig.
For discovering other computers on the network, I like to use nmap. Example:
Be aware that scanning the network with
answered 27 Apr '11, 08:01
All the other answers are correct, depending on exactly what you're after. In addition wireless routers usually have a web management screen with "Current DHCP Leases", which tells you who is on your network. Or at least those that have been given an IP address - it does not tell you those that have allocated their own addresses for which nmap is the answer.
answered 02 Aug '11, 08:40