I use Subler. Yeah, there's no documentation, but if you play around with it, it's very easy to use. Here are the basics:
1.) Rip a movie
2.) Launch Subler (you'll see the Subler icon in the dock)
3.) Open Finder and locate the movie file you want to tag
4.) Drag the movie file to the Subler icon on the dock - Subler will open
5.) Click on the magnifying glass icon in the top right corner
6.) Type in the movie name that you're looking to tag - hit enter
7.) Select the tag file you want to use - hit the "Add" button
8.) Clicking any blank line under "Chapter Track", etc., will show you the "Metadata", "Artwork", and "Other Settings" buttons.
9.) All of this info can be manually edited by double-clicking the field
10.) To change the artwork, double-click the artwork field, and hit "delete" to clear the field. You can then find artwork online (I prefer themoviedb.org), copy the image, and paste it into Subler's artwork field using "Command-V"
11.) Note: for those who intend on putting their movies on the iPad, check the "Create Preview Images" box under Subler's preferences. This will create those chapter preview images that you see for iPad videos
12.) Once all of the tagging information is to your liking, select "File-Save"
13.) Important: after you save it, select "File-Optimize" to finish the tagging operation
14.) Your file is now tagged. Enjoy!