I like halfamoon too, as well as fandomtrees (and fandomgiftbasket too!). That is too bad about nightonficmountain - it sounds like fun. I understand why it happens, but it is always a shame to see beloved events fade out.

Some of my favorites are:
poetry_fiction, a fest where you get a snippet from a poem of the year's featured poet to base a fic off of
newyearcntdown - a fest in December with prompts leading up to New Year's
no_true_pair - where you sign up with list of characters, a set of prompts is posted that uses all the characters in different combinations, and you create works using those characters.

There are definitely certain exchanges I look forward to every year because their themes contain some of my favorite tropes, like hurtcomfortex, pine4pine, and justmarriedexchange.