I've gotten heavily into writing drabbles these past couple of years and Open on Sunday has become my go-to spot for finding prompts.
Advent drabbles, while only active in December, provides an excellent chance to be hectic and write a drabble a day for a month.
Another chance to be hectic and write like the wind is provided by SB Fags End Halloween prompt: Witches' Brew. There's not only a limited time span but the drive to beat the other two teams. Quite fun.