The best GPS laptop for your particular situation is going to depend upon your budget and how you intend on using the GPS navigation software. Laptop manufacturers don't actually design laptops just for GPS navigation. In most cases you'll need to either add the GPS software as a customized option when buying direct from a laptop manufacturer or you'll have to purchase the GPS navigation software separately and install it yourself onto your laptop computer.
Microsoft Streets & Trips 2008 with GPS locator and Microsoft MapPoint 2006 with GPS locator are two of the more popular GPS navigation software packages you will see on the market. Streets & Trips usually goes for under $100 while MapPoint is priced closer to $300. Many online laptop stores offer GPS software separately from the purchase of a new laptop, but I know of at least one laptop manufacturer that allows you to add GPS navigation software during the customization of the new laptop you're going to buy.