Where to find Robot Parts

I have a standing question of: where do you get parts... 

(PS the adds on the right side are Google generated but I don't specify them. Currently this website is unsponsored and clicking on the adds help fund research displayed on the website)

Most of the FRC specific robot stuff(chassis, wheels, etc) comes from Andy Mark

http://www.andymark.com/Default.asp

The metal has been coming from:

http://www.onlinemetals.com/

Most of the Hardware nuts and bolts (literally) come from http://www.mcmaster.com/

For FTC: 

Hardware:

http://www.legoeducation.us/eng/categories/products/high-school/tetrix

Sensors:

http://www.hitechnic.com/

Traditional Electronic suppliers: 

http://www.digikey.com/

http://www.alliedelec.com/

http://www.mouser.com/

http://www.newark.com/?CMP=KNC-G-BRND-Newark&mckv=s7p3ob6Qr|pcrid|10541261421|plid|

I have to give a shout out to Sparkfun! They are an awesome resource for DIY electronics.

http://www.sparkfun.com/

A new China Based factory direct website for electronic stuff.

http://www.seeedstudio.com/depot/

The "how do you know what to order" comes from working with experienced people who show you the way... or hours of online searching, and every once in a while, trial and error.

A cool list for DIY stuff

http://www.wired.com/design/2012/04/top-10-places-to-find-diy-supplies/