Mike Clelland’s illustrations are relentlessly cheerful. The lines are so relaxed but precise and I love the heavy use of arrows and labels:
mike clelland's illustration of a snow cave

mike clelland's illustration of a pulley system

mike clelland's climbing illustration

Tumblr and tumblogs are great, but the attribution can be shoddy. I had to click my way back through 4 or 5 websites to to get to the primary source for these really cool illustrations, No Hugging Is So Hard. [sorry, I lost track of the vias, but the next-to-last was startdrawing]