I now run WoW on a newer 2 gig dual core Macbook Pro. After installing windows and putting 2 gbs of ram in the thing it runs just fine.

Overall cost me ~$2000

I have a 15.4" MBP bought about five months ago, cheapest model, an extra gig of RAM. All details maxed except shadows/glow effect, widescreen 1280xsomething resolution, windowed mode, running XP. 30fps solid in raids fine. Shave off 5fps or so if you run it natively in OSX with the same settings. Add 5fps if you game in fullscreen.

Currently I have a 1.5 Pentium M with 512MB ram with 64 megs of those going to an intel extreme graphics chip (which blows).
It runs wow, but that's about it.

Basically WoW runs on any PC you can think of, it runs good on an amd 1600+ or an AMD 4000+ or any recent notebook, only requirement is a decent videochip (with it's own memory).

Best buy atm would be some high end Dell/Toshiba/IBM or the new Macbook Pro which was boosted yesterday :).
I'm saving up for a MBP 2.33 GHz Core 2 Duo and as of yesterday it has the Core 2 chip and the second model has a 2.33 GHz proc and 2x 1 GB of ram in it. It used to be a 2.16 GHz Core Duo with 2x 512MB ram.
My guess is that it should fly on the native 1400x900 reso but i'm hooking it up to my Dell 24" screen and even that should work.

Oh and a friend of mine bought on of those Dell XPS notebookes (m1700something) and it ran brilliant. Full FPS in 5 mans (60) and orgrimmar. Unfortunately I haven't been able to test raid situations but it should do fine there as well.

I actually bought my laptop two weeks ago(still waiting for it to ship) for $2400. Alienware had an excellent deal at the time, where if selected NVidia® GeForce™ Go 7900 GS, you would get a second one free. Here's what my baby looks like:

[1] Aurora™ m9700

Processor: AMD Turion™ 64 Mobile ML40 2.2GHz 800MHz FSB 1MB L2 Cache
Operating System (Office software not included): Genuine Windows® XP Home Edition with Service Pack 2
Chassis: 17" WideXGA+ 1440 x 900 LCD with Clearview Technology - Saucer Silver
Motherboard: Alienware® NVIDIA® Mobile SLi Chipset
Memory: 2GB Dual Channel DDR SO-DIMM at 400MHz - 2 x 1024MB
System Drive: Single Drive Configuration - 120GB Serial ATA 1.5Gb/s 5,400 RPM w/ 8MB Cache
Optical Drive: 24x10x24 CD-RW Burner / 8X DVD Reader
Video/Graphics Card: Dual 256MB NVidia® GeForce™ Go 7900 GS - SLI Enabled
Sound Card: High-Definition Audio with surround sound
Wireless Network Card: Internal 802.11b/g WiFi Card
Communications: Integrated 10/1000Mb Gigabit Ethernet & 56K V.92 Modem
Bluetooth: Integrated Bluetooth® Device
Primary Battery: Alienware® m9700 12-cell Lithium-Ion Smart Battery Pack
Warranty: 1-Year AlienCare Toll-Free 24/7 Phone Support w/ Onsite Service
AlienRespawn: Alienware® Respawn Recovery Kit

So at this point I'm looking at 2ghz+ processor, a gig of ram (expandable for TBC), 256meg minimum graphics card, 17 inch screen (1920x1200 rez), 80g hd, and wireless that works.

Looks like there are lots of options...

But can I get it for less than 2 grand?

We'll have to find out.

I got an Asus W3J. 14 inch wide screen monitor, duo T2500 processor, 2 gigs of ram, and a radeon x1600 graphics card for $1700. So far I love it, runs wow silky smooth. Runs everything else just as well too. Plays BF2142 way better than my 3 year old desktop does.