Often when I'm coding I load up Photoshop just in order to determine the width and height of an img. My Finder used to show width and height in image preview but as of late that's stopped working. No idea why.
Is there something great that can generate a contact sheet with filenames and dimensions? What do you all use? Maybe a nice appleScript of some sort?
The Finder should suffice for this information. To make Finder show the width/height beneath a file's icon, you need to checkmark "Show Item Info" in Finder's View > Show View Options (Cmd + J).
I find using column view in the Finder is helpful as well.
The Finder's Get Info window will also show image dimensions.
Thanks, that worked really well. I didn't realize that cmd+j had specific option depending on your view.
To add to Scotts answer, it seems you may need to choose Icon View first (Cmd + 1), then use Cmd+J to bring up the "Show View Options". Then you'll have an option for "Show Item Info" which will display the image dimensions.
I never really noticed it before, but this option does not appear to be enabled for List, Columns, or Cover Flow views.
I don't see image dimensions in the Get Info window using 10.5.8, but maybe I'm not looking hard enough?
I use Path Finder. It shows the dimensions, bit depth, layer names, exif info, etc. in the preview pane.
The Finder technique above can be achieved in Pathfinder as well.
You can also open the image in a browser and it will display the dimensions in the window title.
My answer above is for those who prefer to use Finder views other than the icon view (I personally prefer the column view) or if Get Info also stops displaying image dimensions.
Get Info (Command-I) shows the images dimensions under "More Info" (the triangle for which may not be turned down).
Also when an image is open in Preview, a much smaller start up than Photoshop, Get Info (Command-I) from within Preview gives information about the image, including dimensions.
"Determining" hmmm, depends upon your use. Exiftool  gives you all kinds of options. Image::Image-Size  also is handy. Both can be combined with something like FastScripts  to get sizes via contextual menu or hotkey.
I'm not sure of a utility, but the dimensions you used to see are added via the Spotlight index. It seems that the dimensions are being blocked by Spotlight's privacy settings (odd, I know).
To get these dimensions back add the folder(s) under the Privacy tab in the Spotlight System Preferences, and then remove them so Spotlight will re-index the files in those folders. The dimensions should show up again after Spotlight finishes re-indexing.
You can use this technique on as high level folder as you would like, but that will require a longer time to index as there will be more files to scan.
I'm not sure why it says I have -1 points for this answer, as I didn't answer the direct question but rather solved the issue that lead to the question...