Hi Dave,
The weird tilts in architectural photography can be caused by a number of things, but usually the primary culprit is keystoning. Keystoning is caused when your sensor plane is not kept parallel to the plane of the object you are photographing. There's a decent graphic that describes this effect at this link: http://www.cambridgeincolour.com/tutorials/tilt-shift-lenses1.htm (http://www.cambridgeincolour.com/tutorials/tilt-shift-lenses1.htm) The only way to avoid the effect of keystoning is to keep the lens parallel to the plane of the object, or to us a perspective control lens as described in the article.
Here's another link that talks about perspective control, with a few more illustrations, and a short tutorial on how to correct the perspective using software. http://www.flickr.com/groups/afterclass/discuss/72157621501336010/ (http://www.flickr.com/groups/afterclass/discuss/72157621501336010/)
You can correct perspective in Photoshop by using the crop tool, checking the "perspective" box and then dragging in the corners of the cropped area so that the borders of the crop are parallel to the converging lines in the image. An even more powerful way of correcting the perspective in Photoshop is through the Filter>Distort>Lens Correction dialog, and using the transforms for vertical and horizontal perspective. Be careful about "over correcting." As the article referenced above cautions, overcorrecting even slightly can often look worse than no correction at all.
In the following example, I photographed the architectural detail at Glen Eyrie from ground level, and had to tilt the camera up in order to include everything in the scene. When I reviewed the image on the computer, the vertical tilts (keystoning) bothered me, so I went back the next day and photographed a similar scene from a nearby stairway, trying to keep the sensor/focus plane parallel to the vertical lines of the building:
(http://spiritofphotography.com/coppermine/albums/userpics/10001/20100715_102418.jpg)
First shot with lens tilted up
(http://spiritofphotography.com/coppermine/albums/userpics/10001/20100715_103311.jpg)
Reshoot with the lens/sensor plane more parallel to the vertical plane of the building. (There's still a bit of a tilt in order to get the framing I wanted, but not nearly as severe as the first try.)
Note that the horizontal lines are still converging towards a vanishing point (in the bay window for example); however, our minds are able to translate that perspective cue much better than the tilted verticals.
In the next scene, I walked up a nearby path in order to minimize the amount that I had to tilt up the lens, however I still had to tilt the lens some in order to frame the scene the way I wanted to. The inward lean of the portion of the building on the left bothered me, so I corrected most of the lean using the Filter>Distort>Lens Correction>Vertical Perspective transform in Photoshop. I under-corrected the lean just a bit because when I corrected the lines to be exactly vertical it made the building look oddly out of whack.
(http://spiritofphotography.com/coppermine/albums/userpics/10001/20100715_104110.jpg)
As shot, with disturbing "keystoning" on the portion of the castle on the left."
(http://spiritofphotography.com/coppermine/albums/userpics/10001/20100715_104110_pc.jpg)
Corrected with Vertical Perspective Transform in Photoshop (but slightly under corrected to keep the scene looking more natural).
(I suspect this lens has a bit of barrel distortion, which makes fully correcting the vertical tilt a bit more complex.)
Does this help any?
Keith