Being involved in sports events from kid's soccer games to collegiate basketball events and reporting, I am ALWAYS asked (especially by women) what the easiest sports to pick are. A little background, when I was born, my dad was waiting in the delivery room with a golf club in one hand and a helmet in the other. He was certain of two things: 1) that I was a boy and 2) that he would teach me every sport known to man. He was half right and for the next 13 years, I excelled at every sport possible. These days (in my, umm, well, 30's) I continue to play sports and shock and amaze the kids in the neighborhood. Their parents, however, are constantly asking me what sports are the easiest to learn (so they can quickly learn and impress their kids). My answer has to be, none, but the easiest out of all would have to be the following:
1) Biking - While I don't bike as much as I used to, it is definitely one of the easier sports to start. Adding a little extra distance to your best each day is a great way to increase cardio and get in shape fairly quickly. My advice is to check out Craigslist for a bike before you commit to spending hundreds (even thousands) on a Trek.
2) Golf - Ahh, one of my favorites! The good thing about golf is that you'll know rather quickly whether or not you are cut out for it. Another sport that could add up quickly, I advise you to borrow a friend's sticks and buy a good pair of inexpensive golf shoes (my fav's!). The great things about golf is that you really can involve the whole family and from putt-putt to Par 3's, you can find something for everyone to enjoy.
3) Running - Is started running (specifically in the mountains or hilly bluffs) when I was around 12. My father was obese and I was determined NOT to be out of shape or overweight. Since that time, I have helped at least 11 people start jogging/running and have to agree that this is a sport that is simple to start and is extremely addictive. Easy to do anywhere, all you need is a GOOD pair of running shoes (don't skimp on these or your feet will punish you - I'm a New Balance girl myself) and a track or mountain. Begin slowly (1/4 or 1/2 mile depending on your condition) and increase every two weeks.