Some more:

Icon Comms
icontalking a central community for icon makers, with challenges (It also has a sticky listing Icon comms and challenges on Dreamwidth, which would be useful for your list)

iconthat - fortnightly icon challenge comm

genre_icontest - icon contest with a genre theme

icons10in20 - what it says (10 icons in 20 days)

icon_resources


Creative comms
100words - weekly drabble prompt, multifandom

trope_bingo - another multifandom bingo comm

allbingo - central bingo comm for monthly cards and using old cards etc.

tic_tac_woe - mini bingo comm with apocalyptic prompts


General theme/genre type comms (Some of these are v slow, but all still used and okay to post to, to the best of my knowledge, and some fairly active/the mod is def. still around etc.)

britdrama - general comm for British Drama

corsets_and_carriages - general comm for historical drama & fiction

anything_aos - general comm for anything to do with the Age of Sail fandoms

hidden_passages - general comm for Gothic fandoms

mystery_mansion - general comm for crime & mystery fandoms (also includes a sticky with a masterlist of known comms, although it includes inactive ones)

I think that's enough for one comment. I shall make the rest in another!