I'd start with this information:

Server Specs - CPU's, memory, drive configuration, OS, SP level

SQL Server Specs - licensing model (# of licenses), version, edition (standard, enterprise, etc...), SP level, services installed (SSRS, SSIS, SSAS, Full-text), options enabled/disabled (xp_cmdshell, clr, etc...)

Logins

Databases - users, roles

Jobs - when, why, what

Schedules

Alerts

Operators

Those are just some things I can think of off the top of my head.