Sweat It Out

After months and months of seeing the pounds creep up, I’ve decided to do something about it.  For real. 
I’ve joined Weight Watchers (the online version), and I am determined to work out at least three times per week (to start). (I’m also going to cancel my gym membership, since) my apartment complex has a gym and I can do a lot of great workouts in my apartment.
Basically, I want to look like this:
Please note that Miss Brit looks toned and healthy,
not emaciated and sickly.
(After writing all of that I should realize that the pounds haven’t exactly piled on, but it’s easier to do something about it now than to wait until they really have piled on… I’m nipping things in the bud, if you will.)
What are some of your favorite at-home workouts that make you break a sweat without breaking the bank on equipment?