BIONICLE's concept art book got a digital release, so here's a dropbox pdf download of it.
I'd say it's worth taking a look through, even if BIONICLE isn't exactly your cup of tea, since it is pretty cool concept art. And who doesn't like cool robots?
https://www.dropbox.com/s/6dsbhxlqngq6vbi/The_Art_of_LEGO_BIONICLE.pdf?dl=0 