In my opinion, the small membership fee at hirescovers is definitely worth it.
If nothing else, just for all the resource images you can get. Nearly every one of my 1000+ dvds and blu-rays have custom covers, although for most of them, I either make my own from artwork/posters/promo images, or modify a particularly good custom I see, because there's usually some small thing I don't really like about them.
Customaniacs is another good site. I'm pretty sure there was no membership fee there.
If you're interested in custom Star Wars covers, I very highly recommend the forum at
OriginalTrilogy.com It is, for the most part, a great community there, and if you can't find a set of Star Wars covers that you like there, you'll never find one. And you can also find excellent restorations of the original Original Trilogy, as well as many other movies which have been altered from their original state for DVD releases, and plenty of high-quality fan-edits, too.
If you like Doctor Who, there are quite a number of sites with high-quality custom covers, particularly for the new series to match the original series' DVD covers.