The best equipment:

• chair
• monitors
• modern workstation (e.g., nothing older than 2 years)
• ergonomic keyboard

Matching 401k (the higher the match, the better)

Good mentoring.

Freedom to pursue creative outlets related to work projects (i.e., 20% time).

Update: after reading other answers, I think I'd also say:

• private office
• individual book/training budget
• HDHP with the amount of the deductible given at the beginning of the year in the form of an HSA