This is a more difficult question to answer, because unlike a desktop, you are very limited in what upgrades and changes you can make after you buy it. So we are not going to recommend any specific models, but rather what brands of laptops we recommend and the model family they fit into. Before we get into the Laptops, lets talk about the specs we look for:
Quad Core i7 processor
This is the most important feature that will have the biggest impact on your ability to smoothly work with and edit HD footage. Today's advanced video editing apps all tap into multiple CPU cores, especially 64 bit apps like Adobe Premiere Pro CS5.5 or Sony Vegas. Avid has announced that the next version of Media Composer will be 64-bit.
Quadro Mobile GPUs
The Adobe Mercury Playback Engine in Premiere Pro CS5.x is amazing. When you combine it with a mobile Quadro card you will be able to edit multiple layers of assorted HD footage formats in real-time. Avid recommends an NVIDIA Quadro card for use with Media Composer as well. Here is a link to NVIDIA's Quadro Mobile Worktation products. We recommend you select a GPU with at least 1GB of memory and 192 CUDA cores such as the new Quadro 3000M.
17 inch or larger screen size.
If you are going to edit on a laptop, you need the screen real-estate for your timeline, preview windows and tools. For me I simply can't get everything I need on the screen with a smaller screen.
Get as much RAM as possible
Today's NLEs need RAM, the more the better. While most laptops come with 4GB by default, you will be very happy if you get more, go for at least 8GB
Express 34 slot or Thunderbolt
If you plan on adding I/O hardware for your HD workflows, then you need to be able attach them to your laptop. I/O devices like the Matrox MXO2, AJA Io Express or Motu HDX-SDI & HD Express require an Express24 slot. Thunderbolt I/O devcices will begin shipping later this year.
eSata, FireWire800 or USB 3.0
For the fastest possible connectivity for your external storage, we recommend eSata. You can easily attach a G-Tech G-RAID or G-Speed Q. FireWire800 allows you to use smaller portable RAIDs like the Glyph PortaGig. While USB 3.0 is faster then FireWire800, it is our 3rd choice because our top external storage vendors have yet to embrace it. I think they are going to skip USB3.0 and go straight to Thunderbolt.