Iconfinder is a great service when it comes to adding great illustrations to your content.
You can research by keyword, size and licences and thus find a suiting image very fast.
Be sure to read the licences (~free, creative commons, ~free-for-mention, ~free-for-link and paid)
before you use them!
There's are a huge amount of very good images in .svg and .png formats,
you can download it in different sizes very easily,
and there's also an online editor to modify them if you like.
I have been using iconfinder for years, and I have always found something that helped me out.
On other platforms I had to invest a lot of time and/or money to finally find a nice icon or vector image.
At Iconfinder I usually find and download something within a few minutes.
Payment is easy and relatively cheap, though their prices doubled since I got to know them.
But 2,00 $USD for paid vector graphics
still isn't much money if you find an image that you want to use in a professional environment.
Or choose the 9 $USD- monthly pro plan which I consider very priceworthy.
So this is a platform I can really highly recommend. :)
btw: you'll get a 50% discount if you choose to join the iconfinder pro offer.