Backing up sunny staines recommendation read the guys home page: click here for my money (which is nowt as the program is open source and does not even require to be installed) he knows what he is talking about.
Diskeeper 2008, would be my choice. I use it and really like it. It's got a lot of features, performs very well and is extremely convenient to use.
I've also tried Auslogics (rubbish) and JKdefrag (confusing), and there is no comparison. Diskeeper is a far superior product, especially if you are using (or will be using) it with Vista. You can check out the features of the new versions of Diskeeper at click here and download the free trial versions to make up your own mind.
I agree with SUNNY STAINES jkdefrag is very good. MAGHEMITE, I wonder if you would explain what you mean by "confusing" as jkdefrag doesn't need to be installed and is an automated "one click" operation. If you use jkdefrag in conjunction with a file defragger programme( free ) called DEFRAGGLER then you have the best combination in the world.