We go to LV at least once per year and have a ton of player's cards. We normally rent a car and will go to a lot of the casinos off-strip.
The best couple of trips were the first years we had the American Casino Guide (book with coupons you can buy) ... lots of coupons for free play when you sign up for a players card. Many other coupons for 2-for-1 on buffets, etc if you have a players card.
Keep in mind that many of the strip properties use the same card ... MGM Mirage has Mlife cards ... good at NYNY, MGM, City Center, Excalibur, etc
The CET/Harrahs properties have the another card for their casinos (Cesears, Planet Hollywood, Paris, etc).
If you are new to Vegas, you might learn a lot from reading the Unofficial Guide to Las Vegas.