"MacOSX ssh client is based off OpenSSH.
ssh -D <port number> username@remote.host
You want the -D flag for dynamic application-level port forwarding.
From the man-page - http://developer.apple.com/mac/library/documentation/Darwin/Reference/ManPages/man1/ssh.1.html
Specifies a local ""dynamic"" application-level port forwarding.
This works by allocating a socket to listen to port on the local
side, optionally bound to the specified bind_address. Whenever a
connection is made to this port, the connection is forwarded over
the secure channel, and the application protocol is then used to
determine where to connect to from the remote machine. Currently
the SOCKS4 and SOCKS5 protocols are supported, and ssh will act
as a SOCKS server. Only root can forward privileged ports.
Dynamic port forwardings can also be specified in the configuration file."
