The layout of the sponsors on a shirt can be done a hundred different ways. It depends on how many sponsors will be on the shirt. Typically, what I have experienced is the sponsors will be listed in just one color on the back of the shirt. If it is just one or two sponsors, of course they will get more room and be larger. Logos are always nice if available. (Getting people to send you a "usable" logo is a enitirely different thread!)
If there are around 5-8 sponsors, I will typically stack them one on top of the other down the shirt (possibly in order of importance or donation amount). If you have 10+ sponsors you will probably need to create 2 columns. If you want to be more creative you could take the sponsor names or logos and just scatter and stagger them randomly on the back of the shirt....or you could run them listed in a spiral on the back of the shirt. As far as layout is concerned, really the possibilities are endless.
When the shirt has sponsors, I will usually try to be one of those sponsors (sometimes I can get this done by donating the screens on the project or by offering some other type of discount. At other times the customer will just tell me to be sure to include my logo, since I'm printing the shirts.) I like to put my logo at the bottom of the list. I leave the top for someone else and I don't want to get lost in the middle and not be seen...so I've found the logo on the bottom stands out just as much as the logo on the top... the logos in the middle of the mix can get lost.