There are forms of SETI besides the listening-for-interesting-signals kind. Looking for large-scale artifacts also exists:

http://home.fnal.gov/~carrigan/infrared_astronomy/Fermilab_s...

http://www.space.com/24269-how-to-search-for-alien-civilizat...

I find these fascinating: let's consider the branching tree of ways civilizations might grow and then look for evidence for leaves on that tree.