Perhaps it depends on your market? If it's children who are sponsoring (or the sponsorship being for them) they I think thinks like keyrings etc can be good! For adults it's prob more about information, so updates every 3 months of something - but I personally would be just as happy with this over email
I guess the important thing is the work out how much you are going to charge and then what % you want to spend of this on the "gift" element!
As you say different levels of sponsorship could be good as well - Gold - Silver - Bronze etc! But that would start to get more complicated and time consuming to organise!
I also like the idea of "sponsor a hutch" as opposed to a bunny
I was thinking about this a while ago and came up with the following list:
Keyring - 60p (you can buy make you own ones off of ebay and they just a simple home printer will do the rest!)
Photo - 40p ? depending on size?
Information (specific to bunny and general to rescue) - Free (ish)
Postage - 48p?
Updates by email - Free
Total = £1.50 ish!
Extras could be Birthday Card (with photos of bunny) = £1 (incl postage) (home printed from inkjet cards you can buy from WHsmiths ect).
Xmas cards as above!
Calendar (£4.5)/ year chart (80p) - all including postage!
I'm not saying you should charge for each any of these things or anything, I've just spend some thing thinking about stuff like this when I was doing the calendars etc!
Not sure the costs are 100% accurate as I'm at work and can't remember the specifics!
Sorry I've gone on a bit there! Might have deviated from the point
If anyone needs a hand in organising sponsorship packs - printing and posting etc, let me know
If it can be done from a distance of course as I don't live that near to any of the rescues on here!
Hannah