orcishgamer: I'm thinking of KSing this to a rather insane level, even for me, someone for the love of Odin talk me out of it.
Assuming you are interested in physical rewards, there are currently 2 interested tiers that give you decent bang for your buck. The $110 (119 slots left) or $135 unlimited one, which gets you the collector's box, and then the next interesting one is the $500 (since the only bonus of the $250 is if you are interested in the Pen and Paper Numenera, or want the novellas printed). After this, you mainly double your pledge for the next physical reward, so unless you wish to design something for the game, $500 is the top that makes sense.
Unless you do have the 5 grand to get a leatherbound signed Numenera corebook, in which case I hate you...