I quite like Ashampoos magical defrag.
You install it, and forget it. It detects when you're not at the PC, and only works then.
Handy for me as I don't like too many resources being used, and it's only defragging when I'm not sat at the computer working/playing etc.
Gives you weekly reports on whats its done etc too.
Edit: Looks like you get get a free trial too from their official site.
Auslogics is just that, are you on XP ? if so go for that.
Whilst the Vista defragger is very limited on the GUI front (LOL!) it does do the job fine and if you enable the schedule then it will defrag in accordance with that schedule and also Vista will automatically optimise disks when the system is idle if disk optimisation is needed which is neat.
I've used Auslogics, Diskeeper, O&O, PerfectDisk and Vopt on XP and Vista, on Vista I prefer to just have Vista defragger autodefrag every morning so I never have to worry about it.