I was looking at the NASA image of the day today, and it made me wonder about the windows on the ISS. I often see pictures of Earth taken from the ISS, but I was wondering if they had any windows that looked "up", towards zenith, opposite to Cupola with windows facing "down", towards nadir.
There are windows on Zvezda from which you can see zenith, but these aren't facing exactly zenith. It doesn't seem as though any other segment on the ISS have zenith windows.
From this website, at the bottom there are attachments that show the various cross-sections for Zvezda. It's a little confusing, however, since this image has the +x and +z labelled as though you were looking at it from the +y direction, not from zenith. Based on actual photos of Zvezda, however, this image is indeed zenith. As you can see, windows 12 and 13 on the neck of the craft are pointed at a 45 degree angle towards zenith. This 3D model of Zvezda shows the two closed windows, on the neck near the orange circle. You can clearly see window 12 facing at an angle towards space.
This is the best actual image I could find of Zvezda in space (it proves we are looking at the correct side), but unfortunately the view of the windows are obstructed by the body of the craft.
So in conclusion, it doesn't look like there are any windows facing exactly zenith, but there are two that angle in that direction.
The RSC Energia has recently published a study on the effect of high-velocity impacts of meteoroids and space debris on glass windows of the ISS in their "Kosmicheskaya Tekhnika i Tekhnologia" quarterly journal.
At page 55 they have a nice three view scheme of Zvezda windows locations with the sizes, directions and angles specified:
Figure 1. Service module windows (location, Type):
1 — TSK.316.02.000 (∅228); 2 — TSK.316.02.000; 3 — TSK.316.02.000; 4 — TSK.316.03.000;
5 — TSK.316.02-1.000; 6 — TSK.316.02-1.000; 7 — TSK.316.02-1.000; 8 — TSK.316.02-1.000;
9 — TSK.316.01.000 (∅426, uncoated); 12 — TSK.316.02.000; 13 — TSK.316.02.000;
14 — TSK.316.02.000; 26. — TSK.316.03.000 (∅80);
There are many windows on the ISS. Destiny (The US Lab, between Node 1 and Node 2) has a 20 inch window facing Earthwards.
The Russian segment has several, and they have covers to protect them when not in use.
Zvezda is the key module for windows:
Zvezda has 14 windows— There are two 9-inch-diameter (230 mm) windows, one in each of the two crew sleep compartments (windows No. 1 and 2). Six 9-inch-diameter (230 mm) windows (No. 3, 4, 5, 6, 7 and 8) on the forward Transfer Compartment earth facing floor. As well a 16-inch-diameter (410 mm) window in the main Working Compartment (No. 9) and one 3-inch-diameter (76 mm) window in the aft transfer compartment (No. 10). There are a further three 9-inch-diameter (230 mm) windows in the forward end of the forward transfer compartment (No. 12, 13 and 14), for observing approaching craft. Note: Window No. 11 is unaccounted for in all available sources.
The US segment has some windows, but the primary viewing location in the Cupola, which is attached to Node 3, which faces off the main line of the station. The Cupola is facing down, (nadir) towards the Earth, but it has a main window facing out, and a series of windows around the edge.
Thus you could look over the limb of the Earth to see space.
Very late to the party, but here's a supplemental answer supporting the argument that Service Module (SM) windows 12 and 13 can be used to view the zenith.
This shows the location of SM window 12. I highlighted the foot restraint above it (in the zenith direction) in gold as shown.
This shows the view out of the window looking zenith-wards. You can see the gray Strela crane and just a bit of the gold foot restraint.
This shows the location of SM window 13. I highlighted some Russian gadget called BKDO above it (in the zenith direction) in gold as shown.
This shows the view out of the window looking zenith-wards, including the BKDO.