How heavy are you and how old are you? Are you in decent shape?
The reason I ask is because for several years, I kinda let myself go as well. I drank/ate too much, sat my ass on the couch and eventually, got to the point where I'd nearly lose my breath walking up the stairs. I wasn't even obese or anything, just lazy. At my heaviest, I was 6'2", 236lbs. But I wrestled in college at my leanest and meanest 65 lbs lighter. Well, I tried the gym, but unless you're a gym rat, this is basically useless. I mean, it's good to be active no matter what you're doing, but the gym isn't the thing that will get the results most are looking for. If you lose 500 calories in the gym, which is a hard frickin' workout, you usually just add that food to your diet and maintain your weight. 3500 calories = rougly one lb, which means you need weeks of crazy hard work and discipline to lose what amount to 5-10 lbs. You will tighten up very, very gradually, but without the right diet, this isn't even a given. Your metabolism plays tricks, you skip some workouts every now and then to watch a Thursday night MAC CFB game, you let your diet go or have a few extra beers here and there, and you never get to where you want.
Now the guys in the gym that look like we want to actually enjoy the gym. They go there because it's their hobby. Like hunting, coaching little league, playing the guitar, or riding a motorcycle, these guys just like going to the gym. If this is you, you know it and you're not fat because this is what charges your engine. Most men, and especially guys like us who gamble, are extremely competitive. We want to win, above all else. It's subliminal to want to have a better car than your neighbor, a hotter wife, and more money. You can deny this, but it's true for 99% of us. Unless you're a wierdo, you're not going to call the neighbors over to show off your pecs or lift your shirt up at work to show off your abs.
So...where am I going with this? You need to find a way to compete at this. If you do this P90x or Insanity thing, you need to pool together 4-5 other guys, throw a unit or two in a hat, and play for most bodyfat percentage lost or lbs as a percent of total weight. If you want to take up riding a bike, you need to find a local race 3-6 months out that you can train for. You need to set a goal for yourself for that race and find people in your area who also ride that can push you and vice versa.
Since I wrestled, I just took up jiu jitsu about two years ago. It was a smooth transition. Every class, I want nothing else but to dominate my training partners. And because of this, I watch what I eat, I drink more water, I run outside of class, etc. Now, I compete 4-5 times a year in local competitions and have my first MMA fight hopefully in December. I weigh between 190-195 and without bragging, my before and after could be on one of those infomercials. But I definitely couldn't wake up an hour early every day to get yelled at by my TV screen and take it as seriously as I do my training.
Anyway, I'll step off the soapbox. Hope that helps.
