The Mesa Family YMCA is a great value.
I admit, big expensive fancy gyms turn me off -- I hate feeling like I'm walking into a Scottsdale Club when all I want to do is work out in my crappy workout clothes (seriously: I don't have enough money to waste it all on clothing that I wear to sweat in -- wtf?).
That's why I like the Y. It's close to my office, so I often stop in after work. They offer a lot of classes, and the yoga and kickboxing ones I've been to are very good. I've also taken their water aerobics classes with one coworker -- everyone else was about 80. It was awesome!
They just updated their weightlifting equipment and their exercise machines are OK. Basically, this gym has everything you NEED, without a lot of extras -- but that's ok with me. Everyone is pretty friendly, too.
One downside is the neighborhood -- My car got broken into in their parking lot last year and I lost a TON of stuff, so beware!