Favorite building/fine motor toys?

DS spends a lot of time putting random stuff together with zip ties, rubber bands, ropes etc. For example his latest "rocket ship" was built out of a ladle, the pipe for his SVN machine, and a toy ladder tied together with couple of my hair ties. DH and I decided it was time to get him some new creative, building toys. I was really excited about Tinker Toys until neither Target nor Walmart sell them anymore. And can I tell you how disappointed I was to walk up and down the aisles of Target to find that besides Legos there really aren't many toys like that.  I figure there are probably some really cool building/creating toys out there and was looking for some recommendations before I randomly select something online.