I'm looking to build a mobile recording setup with an 8 channel AI. I have Sonar X3. What laptop should I buy that will handle the 8 channel AI.

Try to get one with 2 internal drives, or 1 internal drive and an eSATA port, either an i5 or i7 CPU (or beefy AMD but Intel is a bit faster, in my opinion), and if your primary drive can be SSD then so much the better.  Shoot for at least 8 GB of memory, and 16 or 32 if available and within budget.
 
Having 2 drives is a good thing for balancing access demands - primary drive for OS and applications, 2nd drive for data, projects, audio, and sample libraries.
 
Primary drive of SSD type will give you good performance for Windows - this is not critical, it it means you cannot then afford a second drive or enough memory.
 
Secondary drive either internal or eSATA would be ideal, with USB 3 being viable though not best.
 
Memory COULD run in 4 GB, but really - consider 8/16/32, with 32 being a luxury - 16 is fabulous, and 8 is still good.  
 
When you DO select a laptop, please note that you will want to temporarily disable or if there is a hardware switch turn off your Wi-Fi adapter just prior to launching Sonar, and then you can enable it again after finishing your Sonar session.  This is because Wi-Fi adapters can cause MASSIVE latency spikes, which will wreak havoc at attempts to do audio streaming with Sonar.
 
There are lots to choose from - I would suggest you consider getting screen protection and possibly accidental damage protection, as well.  I used to have a Dell laptop that I gigged with, and over a 3-year period just about all the components were fixed/replaced.
 
There may well be other schools of thought on this subject, too, from other forum folk.
 
Bob Bone
 

I bought a laptop from ADK (Adkproaudio.com) that I use exclusively for recording with Sonar.  There is something to be said for having a system that is optimized for the task.  Lots of choices out there, but I couldn't be happier with mine.

HP seem to do great laptops nowadays (I have been tempted recently but so far have resisted). If you are into firewire interfaces the models with in built thunderbolt interfaces should be an extremely attractive proposition.
 
I notice Cake are using them as well (BTW there are cheaper models):
http://blog.cakewalk.com/sonar-x3-our-demo-machines/
 

I have the Sony Vaio Pro 13. It has a super fast PCIe SSD drive. The only other laptops that have one I believe is the newest Macbook Pro and Air. Handles recording 11 tracks of drums no problem. No need for a 2nd drive. No hiccups, no dropouts.
http://www.thessdreview.c...test-ultra-speed-date/
 

Just for recording, I like the idea of a little Windows Slate PC. They are dead silent. I wouldn't want to mix on one though. It would just be for capturing live performances. Also, I don't actually have one.

I concur about the two drives but be aware that there are two different eSATA ports. You'll want the eSATAp kind ideally, because otherwise you'll need a wall wart or an extra USB port and cable for the power.
Here's a good explanation;
http://superuser.com/questions/266761/does-esata-require-power-source
Also, many laptops offer two drives internally now (mine has), often sacrificing the DVD drive (I did). I have an external DVD drive for when I absolutely need one, but honestly it's quite rare nowadays.

What Robert said I think is spot on.

Two internal drives - you won't regret it. You can get an external DVD drive that you hook up with USB when you need it. For audio engineering having two hard drives should take precedence over an internal DVD drive.

Also what Robert said - turn off WIFI when using Sonar on a laptop. It helps a lot to prevent unexpected latency caused by the WIFI stuff.

If you do like me and use the laptop only for recording and not for editing, then you really don't need much.. but with laptops,, all laptops, there can be certain configurations that you cannot get rid of the DPCLAT spikes. There have been a lot a threads on this topic. And my son had this issue first hand. He bought a top of the line Dell and it had red spikes no matter what you did, conclusion is it's something in the bios that cannot be changed. He couldn't return it because it technically wasn't broken according to Dell.
DPCLAT spikes are not on the radar of 99% of the people who own laptops. 
 
So moral of this story is. Take the DPCLAT software on a USB stick and make them run it before you buy any laptop. 
 
PS, I use a 2004 P4 Toshiba with 2 Gigs of RAM. It can record 16 tracks of audio all night long. 
Main thing is I put a 7200 RPM HD in it. That is paramount for audio. Processor speed and RAM mean very little to recording audio, only when you get home and start editing and adding plug ins. Then you need horse power.  So I just transfer the files over. 
 

wruess
..There is something to be said for having a system that is optimized for the task...

Cactus Music
...Processor speed and RAM mean very little to recording audio...

 
I agree. It therefore doesn't need to be a new laptop. An old one can be optimised. My solution would be to purchase a suitable second-hand Dell laptop, wipe it clean and install Windows 7 from scratch. The hardware drivers are always available from Dell's website. I would leave some of the hardware disabled (e.g. Wi-fi, webcam, audio, etc.) and omit installing the associated drivers. Then I would install Sonar plus software needed for recording, but nothing else. I believe that the resulting system would be far better suited for purpose than any off-the-shelf purchase.
 
Not everybody would be comfortable with doing this though.