Gaiam just bought The Firm recently, but not all of the videos are available on Gaiam's site. I usually order everything from Amazon. TJ Maxx usually has a random assortment for cheap. It is hit or miss, but you can get your accessories for cheap there too.
I have about 20 routines total (I have bought one or two videos every year or two for over 10 years now). Here are some of my favorites:
Yoga Conditioning for Weight Loss - Deluxe DVD Edition (2000)
$9.50. It has three levels and you can watch everyone together or select to watch just your level with the modified poses. I watch everyone and then pick what I can do depending upon the pose. My husband does this one with me and he's not a yoga guy. He just picks the pose he can do :) There is one of these for Pilates--Pilates Conditioning for Weight Loss. The link below is for the Yoga one though.
Gaiam: AM/PM Stretch for Health ($12) I use this one several times a week. It has three routines (AM, PM, and then another one under "Extras"). It is shorter than the full yoga one above and is good to stretch out and relax after the kids are in bed. http://www.amazon.com/AM-Stretch-Health-Madeleine-Lewis/d...
Denise Austin's Pilates has two 20-minute workouts on one DVD; One is yoga and one is pilates. Before kids, I would do them back-to-back, then go to volleyball for a few hours. Now, I do just one of the 20-miute workouts. $10.50
The Firm Sculpted Buns, Hips, and Thighs ($6)
This one is great to get your abs, butt and hips back in shape. I used this one a ton after I had knee surgery. It is completely done laying down on the matt, so there is no impact on your knee.
I also have the The Firm's Transfirmer, but that is quite the investment ($50 at Dick's sporting goods when I got it with a coupon). It comes with 6 workouts and two steps. 3 of the workouts are 35-50 minutes and then three of them are 8 minutes each (stretch, abs, and then something I don't use often). I like having the 8 minute ones for when I'm feeling really lazy-who can't make 8 minutes to work on your abs? It is nice to do the stretch one right after I go for a walk, run, bike or a more intense video.