Marks explained it brilliantly. I do personally try to find monetary sponsorship but I have found component sponsorship is far easier to get and can mean you rely less on the supplying company(s). One brilliant site to look at is the Applegate directory (http://www.applegate.co.uk/http://www.applegate.co.uk/). Almost any company (of any reasonable size) useful to the roboteer can be found on this directory.
Also, responding to Marks second question, what did the companies get out of your sponsorship deals? - All companies which offer free help to me, usually in the form of components, get logos on all of my machines, in the pits of some of the events I go to, and on my website. It important to note that sponsorship is a long term commitment for both you to the sponsor and for the sponsor to you, therefore, I advise you choose between offers carefully.