As a Mac user I use Time Machine to backup, I have been asked to provide a simple backup solution for a friend with a PC. They have an external HD and a single laptop, I'm looking for something cheap or free that's simple to use.
Mozy is a free (up to 2GB) online backup service that does Mac and Windows. It even has scheduling software. If it works, you can then pay a monthly fee and you get "unlimited" storage. I use it and it has saved me more than once. I understand you were asking for a more traditional backup service, but I felt this was worth mentioning.
SyncToy from Microsoft is pretty good if all you're doing is backing up (you run it in echo mode)
Another Vote for Acronis TrueImage Home.
It's cheap, easy to use and is far more versatile than the in-built tools. Apart from imaging files and folder, you can create special, protected hidden zones to store your backups. You can activate a boot-loader that makes restoring an image very easy (especially when you have a catastrophic software failure). It has worked well for me under both Vista (x64) and Windows (x64).