My first go to clip art store is KPM Doodles. Cute and CHEAP! On her new website, if you type in the code NEW50 ... you get 50% off. LOVE!
I also really like the clip art from Scrappin' Doodles, though I do wish they would bundle their blacklines and color clip art together.
For cute backgrounds, I usually use Dreamlike Magic.
And one of my newest favorites is Ashley Hughes on TpT! I just got a bundle of Thanksgiving clip art that is super cute and has all the images I needed!
For free images, I will use CLKER or My Cute Graphics but there aren't always blacklines, which I generally need when creating worksheets, so those are in rare cases I need something I don't have.
Those are the ones I use - what do you use? Link up!