For best results join a gym and hire a trainer (they usually give one to two sessions w/a trainer for free to get you going).
For at home results I reccommend lunges. Side, front, back, and all with weights. If you can't do three sets of at least ten reps/side with weights then start with your body weight. Another good one for thighs and butt are squats. It's hard to describe form so just do google searches to find pictures or videos online of the exercises.
Try push ups and sit ups (use your stomache muscles to pull you up, not your back!) too.
If you get a ball you can really do some kick-ass exercises. I use the ball for back extensions, leg raises, V-Ups, sit ups, crunches, even squats; plus, there's plenty more you can do with a ball.
If you plan on using weights, please don't bother with 1#, 3#, and you probably won't even need 5# weights. When I started at the gym I wanted to go to these wieghts, but my trainer made me start with minimum 8# and I did fine so you can too (I started thin, but flabby too).
Thanks for the suggestions. The gyms not going to happen (hello mortgage). I will take your other suggestions and use them. The first thing I'll do is ditch my five lb weights for 8!
Drew - do you have a good website I can go to to see the side and back lunges? I have never heard of them until you talked about them.
I think what she means by back lunges is that you step your foot behind you into a lunge, rather than stepping forward. Right, Drew?
Just make sure you have your back heel lifted off the ground (you'll be on your toes) and your front foot flat to the floor. Don't let your front knee extend over your front toes. Keep your back tall, chest proud, and when you lunge down, both legs should make a 90-degree angle.
Hold hand weights or dumbbells for a little extra challenge.
I have to say that I would walk 3 miles a day and it toned my legs and nothing else. I found the most useful thing is to lift weights. Your muscles tone up when they have to go beyond their normal comfort zone. So when you lift something heavy, you're muscles are going to kick in. I live near the ocean, so I've decided to walk on the beach which adds extra resistance when I walk and then I carry weights also.