Here is an excellent selection of illustrations by Andy Fairhurst from his Geek Kids & Superhero Kids series.
Excellent series of paintings that features an humorous superhero by swedish artist Andreas Englund.
The Boy Wonder is from a series of superhero minimalist posters from American artist Calvin Lin.
A Long Knight and other crazy superhero illustrations by Creaturebox aka Dave Guertin & Greg Baldwin.
Great vintage-looking portraits of the (supposed) ancestors of superheroes by Marvellini Brothers from Italy.