Pando

Need to transfer a large file or collection of files to a friend, coworker or family member? Many people resort to emailing those files only to find out that their email server does not allow for such large attachments, or worse, the recipients mail server won't accept them once you spent the time attaching them to your email and sending your carefully crafted message. 

From Pando's web site: Pando is free P2P software that makes downloading, streaming and sharing large media files fast, easy and fun. Need to email large attachments, IM a folder, or publish your downloadable videos to the Web? Maybe you'd just like to watch full-screen HD Internet TV. Meet Pando.

Pando works on Mac OS X and Windows XP. The recipient also needs to have Pando installed to receive your files, which is free. There is a tool within Pando that you can use to invite your recipients to get Pando or when you send them the Pando files it will inform them that they need to install it as well in order to receive the files.

Check it out at: http://www.pando.com