- Chris Delvo does the Monstrous Mondays challenge on his blog. Some of them are conversions, but he's got new stuff, too. As an added bonus, he collects the monsters every month and adds them to a pdf compilation.
- The /r/MonsterADay community of Reddit.com had a huge series of monsters (mostly original) created by users /u/StoneStrix, /u/Thalate and /u/Solbera. The community's gone quiet recently, but it's still an incredible resource for 5E DMs.
I'd like to see some new monsters. There have been some good repositories, but I guess I should put some content on here. So, without further ado, here's my first contribution: Wormwood, the Treant Lich. (I'm still working out the kinks, so the experience value I have put in is based on the lich's value from the MM; per the DMG, it might be closer to the lich.)