I would recommend Lenovo Thinkpad W520. As you probably know, Lenovo purchased the IBM personal computer business and the ThinkPad brand in 2005. T43/p & T60 were one of the last IBM-designed units.
Note: I own this laptop and it is just my personal view. I faced with a similar choice - solid workstation that will last for years. I bought it as an off-lease laptop for $400. In my humble opinion, it would be very difficult to get something better for this money. This laptop is 4 years old now. Answer is based on a 4284XXX model.
Specification (for versions: 4284W85, 4284E57, 4284B26, 4284A35):
- Processor: Intel i7-2820QM with quad-core
- Graphics: Nvidia Quadro 2000M, HD 3000
- Memory: 8 GB DDR3-1333/PC3-10600 (maximum memory: 32 GB)
- Maximum Battery Run Time: up to 10.80 hours (9-cell) or up to 21.6 hours (9-cell plus Slice battery)
- HDD: 320 GB (Serial ATA/300, 7200 RPM)
- Screen size: 15.6" (Active Matrix TFT Color LCD, 1920x1080, anti-glare display)
What distinguishes this model from the typical consumer laptop:
- palm rest does not bend in too easily under pressure
- solid hinges
- you can open the display up to 180 degrees
Classical Thinkpad keyboard may be a plus for you. Check the difference here.