One of the utility type programs that I use all the time is Unison. It does a very nice job of synchronizing two directories including propagating deletes.

I use Unison for synchronizing podcasts between my Ubuntu 8.04 server (running bashpodder) with my MP3 player (a Sansa Clip).

Files: 

unison.

Introduction

Jungledisk is an excellent application for making backup copies of your data. The way it works is that Jungledisk works with online storage providers to encrypt then transfer your data to the online storage service. Please see jungledisk.com for more details.

Files: 

jungledisk.