Well even though I'm a newbie on here, the first thing I did with my Golf was tint it. Now since I've only had the car a week, I tinted on Monday morning. After a few days of research both online and visiting three different shops, I decided to go with the ridiculously expensive option. I looked at the $150 tint jobs on offer all over town (Los Angeles) but couldn't stop thinking about Huber Optik. It was the best money I have spent on a car in awhile.
It's been pretty hot this week, and my car sits in my driveway baking in the sun. I get in, and I swear it's cooler in there than in my house. I've never had the A/C above 1. The interior won't fade, crack or ever get hot - and yes, it's Titan Black. Perhaps the best thing (and this depends on the law where you live) it's light enough that the cops won't pull me over, yet I get 50 times the benefit of a cheap 15% tint job.
Of course if you're leasing your car or not planning on keeping it a long time, then perhaps it's not worth the investment, but just the energy savings alone are going to more than pay for this over time.