Very good comparison of SmugMug vs. Flickr.

Dropbox

RetroShare is a Open Source cross-platform, private and secure decentralised communication platform.
It lets you to securely chat and share files with your friends and family, using a web-of-trust to authenticate peers and OpenSSL to encrypt all communication.
RetroShare provides filesharing, chat, messages, forums and channels

Megaupload, one of the internet's largest file-sharing sites, has been shut down by officials in the US.The site's founders have been charged with violating piracy laws.