zxart.ee has a really deep archive of ZX Spectrum demoscene graphics. It will also pretty soon be the biggest archive of ZX Spectrum music as well.
I'm a developer of zxart.ee and I offer some kind of automatic sync beetween zxart and demozoo to exchange the information about missing entries and crosslinking all the appropriate works.
There are really many ways to achieve it. If you are interested, then I would help with doing this.
At least we could make a one-time copy of all the scene graphic entries from ZX-Art to Demozoo (original works available, any kind of PNG/GIF can be generated). I doubt that there is something on Demozoo which should be copied to ZX-Art at the moment, since there is not much content on Demozoo yet, but in future it would be also interesting to cooperate and at least keep track of the Speccy-related information flow.
My goal is to spread the ZX Spectrum art entries as wide as possible, making the watching auditorium grow to the maximum.
Please contact me by email if you are interested: firstname.lastname@example.org
I will also visit this thread, but I cannot promise I will do it often.