"The power of imagination makes us infinite." John Muir
Grade-level content-specific resources:
The first resource that any new teacher at my grade level should not be without is Flocabulary. I personally use Flocabulary for homework, for supplementary content that aligns with the subject area modules in the curriculum, and for the weekly news. In my class I had two or more levels that I could use at the same time to customize the work for each student as needed. It's highly educational as well as fun and full of music that the students love.
The second resource is the Teachers Pay Teachers website. I have found exciting supplementary materials for very little money, and sometimes free, that make the content a lot more interesting and accessible. I have found task cards for poetry, for ethos-pathos-logos, writing prompts, exit tickets, and beautiful templates. It has saved me so much time trying to reinvent the wheel!
http://www.teacherspayteachers.com
The third resource is using a "quote of the day." I find this starts the day on a positive note, and I use this as bell work, where students write down the quote and write a couple of sentences about it that they can share. I try to use inspirational quotes, and sometimes relate them to a holiday, or use quotes from people the students will recognize, such as performers or athletes. There are a few different sites I have used to find the quotes, and there are books full of them that one can purchase.