How to Write Find New Lessons
We all have our tried and true lessons. The ones we love. The ones we can teach in our sleep and that the kids look forward to every year. We have tweaked and perfected these lessons over the years and they are the staples of our curriculum. And then there are all the lessons in between these great loves. These are the ones that aren't yet perfect or mandated from above or are just kind of boring. These "in-betweeeners" are the replaceable. However we often find our selves repeating these "in-betweeners" because we just don't have anything better and certainty don't have the time to develop something awesome. This is when lesson plan databases are awesome!
All Teacher
Teachers Pay Teachers - This is like an online lesson plan swap store, kinda like amazon for lesson plans. I have found some real quality stuff and some fluff. Most lesson seem to range between $0.00-10.00 and you can filter your searches with the the free option. You have to create a free account to download any materials. 
Share My Lesson Share My Lesson is a place where educators can come together to create and share their very best teaching resources. Developed by teachers for teachers, this FREE website gives access to high-quality teaching resources, including many lessons aligned to the common core.
ReadWorks This is not one that I have explored much because it doesn't have much for the arts. However, I put it up here because it "provides research-based units, lessons, and authentic, leveled non-fiction and literary passages directly to educators online, for free, to be shared broadly. Best for grades K-6."*
SMART Board Files
SMART Exchange - "This is the big daddy of them all! This site has an amazing plethora of SMART Board files for your classroom. You must sign up for a free account. They are now starting to add some content that has to be purchased, but there are thousands of free Notebook files. Keep in mind you must have SMART Notebook software on your computer in order to open any of the files. It can be downloaded for free here. Choose version 11.4 for Windows or Mac if you want to be able to use it beyond 30 days."*
Harvey's Homepage -"Teach elementary or middle school math? Run on over to this website for some very high quality FREE Notebook lessons for math."*
Art Teachers
Artsonia Lesson Plan Database
For my fellow art teacher friends you might be frustrated by most of the data bases because the lessons offered are not the deeply rich Discipline Based Art Education (DBAE) lessons that you are looking for. So again I direct you to
Artsonia.com. Honestly if you are an art teacher reading this blog you know my love affair with Artsonia and they are well deserving of my affection. Their lesson plans are all written by real practicing art teachers. Most of the lessons are The consistent formate, the advanced search features, and the student example thumbnails are just some of the features that I love about this database. You do need to be a teacher member of Artsonia to access this page, but if you are an art teacher you should be a member of this organization for so many other reasons anyway.
The Incredible Art Department.
This is the staple that has been around forever. Since 1994 (which in technology years is forever) this site has been providing teachers with high quality DBAE lesson for art teachers. These are useally very high end and involved lessons that need a lot of prep. This is a great place to find some new favorites, but for better or worse these lesson tend to be a little "ivory tower." This is good place to look for a new unit, but not for an inbetweener.
*Resource provided by Professor Marcia Jeans of Baker University