Some are already mentioned above
Videolan/VLC or similar players (newest versions)
Mainstream Browser with HTML5 support, Adblock etc. (Firefox or WebKit-based)
3D drivers/capabilities for multimedia and games. Other OS with a smaller audience have started to sponsor drivers. eg. AmigaOS and Radeon drivers:
(Link in German)
Could there be another funding project for 3D drivers on Haiku? Or this already ongoing? I found these links
Longer term, people could start writing 3D games and multimedia on Haiku, that would be great. To me, this was the strength of BeOS for endusers - great multimedia capabilities and responsivness.
I know that this is some time off, but one can dream…
PS: I’m sure people would sponsor for 3D/multimedia development if needed.