Easy to use MAC Network Analyzers

Hello, This is my first post on this forum. I am new to the Macintosh hardware/software + networking. I am looking for tools to monitor network traffic on my new MacBook. I would like to avoid running linux or Windows in a virtual machine just for this function.
Any suggestions from the community?
If there are any free programs that would be great as my IT budget is...well I would rather not say.

Thanks.

http://www.wireshark.org/

or

http://www.obdev.at/products/littlesnitch/index.html

The first is really more of what you are looking for.