I will add ones that i've discussed with you already and a few others.
1) More options on what to display, and where to display it with regards to the total donations received/needed etc. It seems lots of mods add into the sidebar, and it can get cluttered and messy, So possibly having a choice to display it under the navbar / above the forums would be a nice choice.
2) Awards mod integration. Not sure how difficult this would be, on our forums when someone donates, i manually give them an award which says they have donated.
3) Send the user a prewritten PM thanking them, when a donation has been marked as 'confirmed' by the admin.
4) Tiny thing, Have the 'Donate' button on the navbar, show up in a different colour just to make it stand out a little bit.
Otherwise this app is perfect as it is, and is very well created, There's just a few tiny tweaks that would help, but are not important :)