As much as I love using visuals for lessons, there are times when I also want a different kind of image - not necessarily a full blown techni-coloured picture but more of a sketch or illustration, for example.
This type of visual is equally useful and supportive for students, especially when they are preparing a short presentation and may want to add a visual but not necessarily images/pictures.
FreeIllustrations combines a range of sites with vectors and illustrations to dip into.
These can be used in slides, in short videos (e.g. with Powtoons or VideoScribe or any other video maker that you may like); they can be added to documents and worksheets for learners.
As always, it depends on one's context and teaching aims.
Another fun and interesting site for visual support which keeps it simple, (but fun) is 3D Hands Gestures.
Lastly, and though this is far from new, Google Arts & Culturemediums , themes, art & culture experiments, this is a rich resource for learners and educators alike.