Hi @pserra
I try to tag all the citizen science datasets I can find. The list is available here: http://api.gbif.org/v1/dataset?machineTagNamespace=citizenScience.gbif.org
It can also be downloaded by clicking on this link: http://api.gbif.org/v1/dataset/search/export?machineTagNamespace=citizenScience.gbif.org
This is a semi automated tagging based on this approach: Finding citizen science datasets on GBIF - GBIF Data Blog
I try to update the tags twice a year. It is far from perfect but maybe it can help?
[UPDATE] The machineTag filter is no longer valid or up to date, I recommend using the approach described here instead: Finding citizen science datasets on GBIF - GBIF Data Blog - #8 by mgrosjean