Automoblox (only a little plastic)
Tegu blocks (they have robot and car sets)
Marble run
Ring toss or beanbag toss
Erector/Meccano set

plain old wooden blocks....my kids are late Elementary now and they still incorporate them into their play regularly

Unfortunately, the non-plastic toys are usually quite expensive because they have to be crafted out of wood (or metal, i suppose).

My kids played with this little wooden ramp racer toy, and it was very popular. It is one of the few toys that I plan to keep because it's so adorable.

It was not identical to this but is was similar.
http://www.amazon.com/EverEarth-Jr-Size-Ramp-Race/dp/B00279IZP4/ref=sr_1_1?s=toys-and-games&ie=UTF8&qid=1441216899&sr=1-1&keywords=ramp+race

Wooden toys for 5 year old boys: https://www.fatbraintoys.com/toys/toy_categories/wooden_toys/index.cfm?q=&d1=&d2=&d3=&d4=&d5=&d6=&d7=&d8=5&d9=&d10=&d11=&sf=n&s=1&ld=q&o=1&m=51

Looking for something that will help promote independent play AND is not plastic. I feel like we are being swallowed up by plastic in this house! I started off as one of those anti-plastic people, but ... that didn't last past the first couple years. He's into Legos, Playskool hero transformers (no weapons), has wooden building blocks, doesn't really get into puzzles alone... Any ideas?