I don't know why I haven't contributed here yet, so here's my list. There is no specific order for me, I just write the species down on how they come to my mind.
1. Capybara
2. Leopard (any Asian subspecies, preferably Amur, Persian or North Chinese)
3. European lynx
4. Alpine ibex
5. Takin (any subspecies)
6. Tasmanian devil
7. Yellow-footed rock wallaby
8. Przewalski's horse
9. Goodfellow's tree kangaroo
10. Fossa
11. Coquerel's sifaka
12. Porcupine (crested)
13. Ocelot
14. Maned wolf
15. Common rhea
16. Black howler monkey
17. Any gibbon
18. Sika deer
19. Baboon (preferably gelada baboon or hamadryas baboon)
20. Javan banteng
Thanks for your work
@random goat and good luck for your PhD.
My five additional species are:
21. Diana monkey (we need more smaller to medium sized monkeys and we are totally lacking colourful guenons ingame)
22. Indian blackbuck (more hoofstock especially from South Asia is always welcome)
23. Common wombat (unfortunately didn't get a spot on my 20 species list, so here it gets one)
24. Honey badger (it was a hard decision between this and the wolverine but I go for the African species)
25. Javan lutung (we need more Asian primates and a langur is missing so far).
@random goat: Is it possible to edit the previous 20 species meta list? If so, I would love to exchange the sika deer with the Pere David's deer.