I like the Collector Focus site a lot. For most of my PSA cards, I use the PSA Set Registry. (That way, it helps to know which cards that I am missing for my player sets.) For non-PSA and non-playing days, I use the Collector Focus site:
Link
I have some small pet peeves like the too many links displayed which Danny mentioned. Also you can't really order the cards within the category. Well, it does order alphabetically by the card title. However, if you have the same card title then it's random on which card appears first. For example, I like to show but front and back scans of the card, so both of these images have the same card title, but different card descriptions (2nd line). However, the software doesn't sort by the second line, only the first, so sometimes the back image appears before the front image. I've had to jerry rig it by add dots to the card title to try to get ordering correct. Also, since it only sorts alphabetically, if you want to order by card issue date, it can be more difficult if the date uses circa as: c1915 or c1920s since the circa would immediately sort the card to the end. Obviously, the workaround is to just remove the circa as part of the date.
Finally, as I said, I like to put both front and back scans of the card, and I don't like to merge it into one image. (You lose resolution when you zoom in on the image on CollectorFocus, and the front scan may be vertical while the back scan is horizontal, so they don't always mesh up.) However, for the image for the category, the software randomly picks an image from all of the ones within the category, so half the time, it will choose a back scan, which isn't great.
Anyways, the software is free, and I really like it for the most part, so these are just small issues with the site. I don't really know of others that I like better.