While getting ready for my husband's move to the US from the UK, we've both been digitizing our DVD collections so it's less for him to haul, and I gain extra room for what he does bring. What I'm using to tag the files for easy browsing in iTunes and on the Apple TV is MetaX.
We wrote a tutorial on using the meta-tagging program in 2009, and it pretty much holds true still in Lion. Drag a video file into the program and you can search for associated tags through tagChimp and Amazon, or write your own. If the file isn't in iTunes, it'll copy or add it to your library based on your settings. To edit an existing file in iTunes, right-click the file, select "Reveal in Finder," and drag the file to MetaX. It'll replace the one in iTunes. If you're using Handbrake, you can set the preferences in Handbrake to send a file straight to MetaX once it's done ripping or converting it.
There's a robust feature set in MetaX, including various browsers to aid your search for tags and cover art, a frame grabber if you'd rather use a still from your video file and a barcode scanner for using the DVD packaging to search for tags.
There are a few glitches. Sometimes, the file will have two entries in the iTunes library. Delete the duplicate entry, but do not delete the file. I learned this one the hard way when I accidentally deleted the iTunes copy and had to rerip part of a DVD. The tag search also tends to stop after a period of time, but relaunching MetaX will take care of that.
MetaX is a free download, and it's worth checking out if you're considering digitizing the DVDs you already own.