a. WXGA – 1280x800 or occasionally 1280x768; For people who like big text and icons that are easy to read. Less stuff fits on the screen, which translates into more scrolling.
b. WXGA+ – 1440x900; A modest bump over WXGA. Text and icons are a bit smaller. A little more stuff fits on the screen. c. WSXGA+ – 1680x1050; The middle ground. Again, text and icons are smaller than WXGA+, and more stuff fits onto the screen. Good for having applications open side by side, like a web browser while playing a video.
d. WUXGA - 1920x1200; Very small text and icons, that can be hard to read. Lots of stuff fits on the screen, which means less scrolling. Good for applications that require a high level of detail like CAD or Photo Editing.
I recommend as a high-end business machine the T500 with 3650HD. It is a mid-level mid-range GPU with 128bit bandwidth. The build quality on the T500 is superb, very solid, robust and durable.
About hardware, it has a P series CPU, most likely a P8600 at 2.4GHz and 1GHz FSB 3MB L2 Cache. The GPU is as before mentioned an ATI Radeon 3650HD, capable of most graphic applications. The RAM installed is DDR3. It uses 5400RPM HDDs or 7200RPM HDDs for faster performance. The keyboard on ThinkPads are legendary, and reviews say it is still a top-of-the-line keyboard. The TFT CCFL screen is not as bright as a T400 (the smaller sibling) but it is very good and bright. The T500 offers up to 4 hours on Integrated Graphics, thanks to the switchable on-the-fly graphics it has. You can either switch between Intel GMA 4500MHD and ATI 3650HD whenever, for better battery life or better graphic solution. With 9 cell battery, the T500 reaches 6.5 hours.
Price is a bit high, but refurbished models can be found on that range (maybe you might even need to push it a little bit).
Other great laptop out there is the Dell Latitude E6500 15 inches of power in a rock solid built machine. It is very similar to the Lenovo, but it does not offer switchable graphics. It does have backlit keyboard, which some say it is as good as Lenovo's, it has LED screen for better battery life and they offer a Quadro NVS 160M suitable for 2D graphics applications.
In the Dell Outlet it can be found with great deals, also the Latitude E6400, a smaller and lighter version of the above.
I have never owned an Acer, so I can not really help you on that.
About HP. HP consumer line, aka Pavilions, I find them to be rather weak and plastic-feeling. Whenever I carry one around, I feel like it is going to brake on my hands on any given time, since I have a 2 years old Dell Vostro, which is very solid, I compare almost everything to this (may not be fair). Also the Pavilions, I really do not know what they are made of, but the surfaces seem like pure glossy plastic, and this is...they are fingerprint magnets!
On the other hand, HP business laptops are very solid. Reaching the levels of Dell business laptops and Lenovo's Thinkpad levels on build quality.