OK, I have started putting together some preliminary 'packs'.
See http://meta.wikimedia.org/wiki/User:Pfctdayelise/WikimediaShop & http://commons.wikimedia.org/wiki/User:Pfctdayelise/Commons:Packs
I gather the next fundraiser is coming up reasonably soon, so I suggest that instead of rolling out something huge, we offer something quietly. I think I can probably finalise 2-3 'Commons Packs' within the next few weeks (ZIP consisting of a set of 12 wallpaper-suitable Wikimedian-created images grouped by theme, + a README/licensing/intro/seealso/WMpromo HTML page) - definitely a Science one, plus maybe an animals/insects one or flowers, plus something landscape-y (we have tons of great images like this and I haven't started grouping them yet).
Here's the Science one: http://commons.wikimedia.org/wiki/User:Pfctdayelise/Commons:Packs#Science
According to http://en.wikipedia.org/wiki/Image:Avgsizebyday2005.png , only 3 days out of all the days during the 3 2005 fundraising drives had average donations of US$40. So I suggest we set that as target for this sweetener, to try and lift the average donation to $40 more of the time.
We could then make a statement like "donate more than US$40 and receive a set of 12 beautiful computer wallpapers for free! 3 themes to choose from" and then that would take them through to a download page where they can choose. I don't know anything about what would be technically required here.
Two possible problems there, one is that it might drag down some donations if people were already planning to donate, say, $50, they might think, "Hey, $40 is enough" and only donate that instead. Another possible problem is that it might take away from all the goodwill fuzziness and people will instead think, "Hey, $40 for computer wallpaper, that's a rort. Stuff them" (except possibly think this in a less Australian way :))
So if, for these reasons, all ye foundation-l folk aren't keen to do this, then I have a backup suggestion! Offer the downloads to people who donate above $40 (or whatever), but as a (semi-)secret - don't tell them before they donate. Then we can say, "Since you donated above $40, you receive a free wallpaper set as a special thankyou." I can't see anyone having a problem with this since hey, they already donated...
I guess we would be able to get download statistics, so we would at least be able to see if people are keen to download such things, and we can set up a feedback page obviously and hopefully if people like them they will let us know. If it seems to be liked then I would look at expanding into more "Packs" and cross-project material. And if nothing else, it will promote the Commons ;) and our fabulously talented Wikimedians.
so... ?
cheers, Brianna