I love workout videos! It's pretty much the only way I'll purposely exercise, especially in the winter months. Dinahgirl, I like Karen's Burn and Firm too (only done it once so far, but I know I like it because I like pretty much anything Karen puts out). A great resource for video information is Collage Video. They put out a totally informative catalog.
I'm beginner/intermediate level so there aren't a whole lot of videos that are appropriate for me, but I find them. I began doing them a few months ago again with my sister, and the "homepage" link if you click my username goes to my blog where I blather on about different videos.
Love: Karen Voight, Petra Kolber (to an extent), Crunch (mostly)
Loathe: Denise Austin, Kathy Smith, Donna Richardson
Styles + : low impact, dancy routines, sometimes athletic routines, best music is rock (as on Your Personal Best)
Styles - : fast footwork (I'm not agile enough yet
), ab work!, videos with too-short or nonexistent warmup/cooldown
Also, I thought I loathed Leslie Sansone but maybe I don't. Some days I'd just like to march around and not think too hard—her videos are good for that, right?