I'm personally a big fan of Tony Horton (who does the P90X routines). He also has a series called 10-Minute Trainer for people who are just getting started, don't have a whole lot of time, etc. After the birth of my second child (from which I not only still had 20 lbs left over from my first, but then added another almost 50 lbs with my second), I was extremely depressed about where I was at and needed to do something about it. Some of the initial baby-weight came off before I started the program, so I was up about 50 lbs total from my first kid at the start. Mildly following the dietary guidelines (I like dessert a little too much!) and following the program starting at just 10 minutes a day and working up to 20 and then 30--plus I was still breastfeeding--I ended up losing more than 10 lbs!! The second time through I lost another 5 lbs.
Once I was able to get through the workouts without wanting to throw up, I knew I was ready for the next level and I invested in P90X. I went through that twice, lost 10 more pounds, trained for and ran a 10K race (!!!!), and I'm now training for a 15K with the intent to run a half marathon next spring...and I HATE running!! I'm just feeling so motivated by my new strength and reinvigorated body that I just want to keep it going. I'm not as strict with my eating as I could or should be and therefore I know that I'm sabotaging the full possibilities of weight loss, but for right now, I'm ok with that.
Both the 10-Minute Trainer and P90X are available directly through Beachbody.com. Don't fall for anything marketed as "new" from eBay...they're bootlegs and illegal and are often a bit messed up (I found that out the hard way).
Last, but not least, the dietary guidelines that come with the P90X routine are really awesome. They give you everything you need including a daily calendar of what to eat and the recipes that go with it. And they help you learn how to incorporate long-term changes into your life so that everything you get isn't just a non-sustainable quick-start.
(no, I don't work for Beachbody! I've just been so impressed with what their workouts have done for a number of my friends, coworkers, my husband and myself that I feel I would be remiss if I didn't recommend them!!)
Good luck and whatever you do choose, don't give up! Something is better than nothing!
edit: forgot to mention, after almost a year of consistent work, I'm back to my pre-second child (but post-first child) weight. Another 10 lbs and I'll be at my goal...