Here are some photographs with windows I chose for this post. The first two pictures feature a window as the main subject. The first one is really about the humorous balance between two halves of the window: one side advertising the store with the text "now open" while the other side suggests the store is under renovation. The second photograph features a window in a lighthouse.
2007 - Canon EOS-300D, 1/125, f/8, ISO 200
2009 - Sigma DP1, 1/200, f/8, ISO 100
In the next two shots the window acts as a frame. The first of the two I took in the same lighthouse as the previous photograph.
2009 - Epson R-D1, 1/2000, ISO 200
2009 - Canon EOS-1D, 1/3200, ISO 250
In this next photograph I really liked the window frame. However, with its nasty reflections the window alone does not make for a very pleasant subject. The man sitting on the bench gives it both a context and scale.
2009 - Sigma DP1, 1/500, f/5.6, ISO 400
The last image features an open window, which breaks the pattern or repetition of closed windows. Emphasis is given to the open window by using a tilted lens (essentially this just gives a very shallow depth of field in this example).
2009 - Canon EOS-1D, 1/8000, ISO 320
I used a Carl Zeiss Jena 80/2.8 lens on 1D, a Sigma DC 18-50/3.5-5.6 lens on 300D, and Leica Summicron-M 50/2 on R-D1 for these photographs. The 80/2.8 lens was used with a tilt adapter.