You may only name two parents (one may be a step), your wife and your kids. These folks get unlimited free space-available rides anywhere in the system.
In addition, you may designate one person each November to receive 4 space-a roundtrips. This could be your girlfriend, neighbor, uncle, step dad, babysitter, mistress... whoever.
If you are a good boy and never call in sick, you are also eligible to receive two space-a round trips a quarter to give to anyone. But beware, if this person p's off a customer service agent or tries to sell the pass you've given them, you may lose all your pass privileges for a year.
Pass privileges with other carriers are your standard fare of ID 90 and ID 75s.