Every few months I go to google images and search for 'industrial decay'. I don't know why the pictures I find inspire me, or even what impulse made me first try that particular word combination, but I love the result. The images I find are so inspiring I have a hard time staying focused, so many different stories spring to mind.
I know some steampunkers like glittery brass and cleanly etched lines on the samovar in their manicured Victorian salons, but not me. Give me dirt and grime, rust and decay any day. It's far more visceral and this, is the sort of thing that gets me going (well this and coffee).
S. Marshall takes wonderful photographs, including these of an abandoned French bunker. Originally built in the late 19th century, it was in use until sometime during the early '90s.
Another by S. Marshall, this time of the Rankine hydroelectric plant's tailrace.
Baldo2008 has a fantastic array of photos taken in abandoned factories.
From Staticpulse, a couple of HDR photos of ducting.
To explore the world of industrial decay on your own I highly recommend starting with The Industrial Decay Network