I have been using an Acer 5610z for some time now and it dual boots Windows and Linux perfectly.  Its 15” screen is great for my bad eyes and it’s what I use when I have access to AC. If I am cracking wireless, I use a smaller version with just a 10” screen and a slower 5200 rpm hard drive. When I am auditing wireless I tend to be very mobile so good battery life is important.  Make sure you get at least 1 gig of memory and a decent size hard drive, say 250 gigs or more.   Intel seems to have the edge with CPUs at this time and the more onboard CPU cache the better.

If you want to get the cold shoulder at the next Defcon, I would suggest walking around with a Dell and hand out your AOL email address.  It’s interesting to see how many people there walk around with nice looking small black ThinkPads.  ThinkPads are good but you have to be careful about not holding it by the screen or you can cause it to crack. One thing I can say about Dell is they seem rugged.  I have dropped them and they still seem to keep ticking, but I might have been one of the few fortunate.    However, if you want the image of choice for the leet and if you care about such things, then go with the ThinkPAd.  It always makes me smile when I see nerds trying to impress other nerds, LOL.   

I agree with Ketchup, and have been a fan of Dell's stuff.  I wouldn't mind having a Netbook for it's size, or one of the new thin MacBooks, but that said...

I have used various laptops and equipment for pentesting, as well as everyday use.  

I have an oQo model 2, which is great for pocket / concealability, but it's not functional (without a dock or something) for normal everyday use, and therefore, I would NOT ever make it my primary machine (additionally, it's not the speediest, anyway.)

For everyday purposes (both pentesting, as well as presentations to my customers / peers, etc,) I have an HP TouchSmart tx2-1020us tablet.  Run's Backtrack nicely, and I have both usb and pcmcia Atheros cards for it for WEP and wireless testing.  I like it because:  a.) it IS a tablet, making carrying it around easy with it's 'lightweightness,' size and touchscreen, b.) it has a presentation remote, so I can easily plug into a projector and present on the fly, c.) built-in webcam (when in tablet mode, and walking around, I catch a lot of good 'visual' info about a test site, etc.  There are other reasons I like it, but overall, just a nice little unit.  Certainly, however, it's NOT the most durable, so that's one drawback.  

And for DEFCON, I would very likely carry an older laptop around  ;-)  So long as you can boot Backtrack, has some open USB ports, etc, and it has plenty of memory, etc, just about any laptop is pretty functional these days.  So, as Ketchup so appropriately put it:  " I think that just about any laptop would work, as long as you are comfortable with it."

Most ATheros chipsets can, and there are others.  If the laptop doesn't have one built-in, you can buy an external, just as easily.

I actually like using an external adapter in addition to my built in wireless adapter.  I use my Belkin USB dongle for injection.  I can leave my built-in Broadcom card in managed mode, and my USB adapter in monitor mode.   I find this convenient.

ok, so i should use a external device for packet injection. thanks you guys. I hope that one day I'll have enough experience to contribute to this forum

As far as the onboard wireless available on laptops, I wouldn’t be too concerned.  If you are going to just hack your home router then that’s fine and those laptops that use the atheros chip are usually fine for injecting.  Later when you do professional work you will more than likely find you need a good external antenna. The reason being is hackers don’t attack wireless sitting in the main lobby of a business, unless it’s a mall or airport or something similar.  In my experience hackers sit some distance from the building and attempt to make their breach.  You will find onboard wireless is usually not strong enough to inject from a distance that allows you to be stealth.  I am not saying there aren’t people that are once in a while lucky injecting and cracking their neighbor’s wireless with their onboard wireless, but that is way to “iffy” to be considered professional in my opinion.  You might argue that vulnerability is vulnerability regardless if I do attempt to make the breach sitting in the office of the CEO or lobby of the company or way out at the end of the parking lot, but I would have to disagree.  For instance, I have had a few occasions where I was able to inject and access the wireless while inside the building but the moment I was outside I found it impossible. This could have been due to the kind of paint and metal construction of the building. This particular building had extremely good physical security so it was extremely doubtful anyone unauthorized could get in. Workers there already had access so they had no need to crack it and any terminated employee is escorted from the premises.  How one might write this report might be an interesting topic for another thread. Yes it was vulnerable technically, but was it really?   In my opinion a first class wireless attack has to include a breach attempt from inside and outside the perimeter with a reasonably powerful external antenna. Again, don’t get too hung up with what’s onboard unless you are just thinking about experimenting with your home network, but eventually I would recommend attacking it from outside your house so you can see the limitation of onboard wireless.

Also, if anyone reading this is new to the subject and wants to get started but is looking at cheap or second hand laptops, be a little careful. Linux has come a long way but you still will find it doesn’t always support every chipset.  I would recommend you burn a copy of Ubuntu or Backtrack and try and boot it first to make sure.  Boot it all the way to the gui with startx.   You will save yourself from some headaches.