Used to use edhelper.com. It became overly expensive. I actually was able to create packets for my 3rd grade science curriculum, using edhelper. However, this was several years ago. Now, I create packets with google drive and superteacherworksheets.
I love it. As a social studies teacher it has a lot of great things to read that correspond with what we are learning. It is also great for sub plans should you need to put something together quick.
I really like it for math, vocabulary, and literature units. I pay for 2 years at a time and the rate ends up being less than $2/month. I teach 3rd grade.
Love it for the morning work. I use that all year and I can print out different grade levels. The sheets aren't "baby-ish" so it works for my high school students with disabilities with reading/math on the 1st grade level.