Im using a Dell at the mo, but have just had an HP one delivered to replace it. I think Dell are good reputable machines but they dont have anything what I would call exciting. You get the inspiron range which are the cheap and chearfull home use ones, or the latitude business range which are very powerfull well built machines, that a lot of people I know in the computer industry swear by. Plus unlike most laptops which just come with a 1 year guarantee if you buy a Latitude from a Dell outlet they normally come with a 3 year warrenty, which just goes to show how much faith they have in their machines.
On the other hand like I say with Dell they are boring, but it depends what you want it to do, I like the 'entertainment' laptops which you see more of, with wide screens, built in webcams so you can video call with your MSN contacts, built in digital freeview TV, dvd writers, card readers, so you can pop your digital camera or mobile phone cards in etc for downloading stuff etc. So its worth looking at what sort of features like this you would like.