These are the important things to remember while buying a laptop
The Budget: IBM Thinkpad is the most expensive laptop followed by Sony Vaio. If you can spend around 2000$ then IBM thinkpad is the best laptop to buy.
After Sales: Dell is the best when it comes to after sales. Dell ships laptops within 24 hours and they have a very good after sales facility. This is important because laptop repairs cost a lot of money. Better get a 2 year warranty when you purchase a laptop
Battery Life: This is very important when it comes to buying a laptop. Usually people use laptops for meetings, presentations and it should be able to work without batteries for atleast 2 hours. Batteries also fail very often.
Monitor Size: Laptops with 15 inch monitors are usually preferred.
Keyboard: This might seem very funny but keyboard is very important to consider when buying a laptop. Dell has the worst keyboards.
Weight: IBM thinkpad is the lightest laptop and Dell is the heaviest. If you travel a lot then choose a laptop with minimum weight.
Best Laptops to consider: Toshiba, IBM, Vaio, Dell