Buying a laptop is a challenge - there are so many different makes and models it's hard to choose. Instead of thinking about brands and prices, I suggest you begin by analysing your laptop needs. In my mind, the most important things when buying a laptop are (in no order): Screen Size, Reliability / Ruggedness, Weight, Battery Life, Networking features and Processing requirements.
If you plan on using your laptop at your desk most of the time, then things like weight and battery life won't be important, as you are going to move it infrequently and it will mostly be plugged in. In which case I'd recommend buying a larger unit where you'll likely get a bigger screen and won't pay a premium for portability. If on the other hand you will be travelling with your laptop frequently I'd sacrifice screen size for weight and battery life. Additionally, moving a laptop around a lot can strain many of its part like the screen hinges and casing. If this is your situation I'd go for a 'premium' brand laptop.
Any laptop you have should have built-in wireless networking. Whether you have access to wireless now is irrelevant, eventually you will want to use wireless networking so having it built-in is essential. I'd also get a machine with built-in bluetooth - this way you can take advantage of this other wireless technology without spending extra on dongles. The majority of laptops these days also come with built in Ethernet and a modem (both essential)
Along with good networking I suggest getting a DVD writer, preferably double layer. This will allow you to backup all of your important data - DVD's hold about 5 times as much as CD's and shouldn't set you back too much.
Lastly, when choosing a laptop make sure the warranty is solid - the longer the better. Laptop's have a horrible habit of breaking in the 13's months and are very expensive to repair - an extended warranty can often be a lifesaver. My preferred brands of laptops are IBM/Lenovo Thinkpads or the Apple iBook or Powerbook (now MacBook Pro) - both of these computers are solid, reliable and have good brand support. They also come with most of the features I have discussed above as standard.