It is only in the past few years that I have self-identified as a skeptic or critical thinker. I didn't just wake up one morning and start evaluating things in light of available evidence, though. It was a gradual process and I have a few people and things to thank for it.
Here's the first list.
My Mother: I was raised to think about things rather than just blindly accept them. My mother taught by example more than by lecture. She also presented me with evidence whenever she was trying to make a point. Before every major purchase (car, VCR, appliance) she broke out the Consumer Reports guides and did her own research. She and I both had our woo-woo phases but even through all that she made sure I looked into things before making any decisions. Here's her blog.
My Son: My wife and I were still nominally Wiccans when our son was born. That didn't last long. My wife's post on the subject describes the process of our 'conversion' better than I can. It's amazing how the welfare of a child can turn things around. And I'm not the only one. Dr. Val Jones mentions that seeing children harmed and killed helped turn her from a passive observer of pseudoscience into an active crusader against it.
My Wife: You try not going along with what The Perky Skeptic says.
Seriously, though, she is my rock. She has one of the finest minds I have ever encountered and I'm lucky she's my friend and wife. Her decision to raise our son to think for himself (see above) is one of the best things she could have done for him.
The Internet: There is a lot of misinformation on the internet and I've been burned by some of it. I've never sent money to a deposed Nigerian prince or anything but I have been fooled by various rumors in forwarded emails, etc. This sort of thing didn't start with the internet, of course, but the sheer volume of information makes it more likely that a given person will be fooled eventually. You throw enough crap at a wall, something's bound to stick.
That same volume also sped up my journey towards skepticism. Tale after tale proved to be false or heavily embellished. Eventually, I learned to run things past sites like Snopes and that helped immensely. The 'don't believe everything you read' concept was blasted into my brain through several brute-force attacks and finally took.
Roleplaying Games: I have been an avid gamer since I was 12. One of the first things a gamer learns to do is to implement house rules. These divergences from the official rules of a game can be as small as ignoring encumbrance ratings to as large as creating a new magic system. RPGs taught me that just because something is written in a book you don't have to follow it to the letter.
I leave the discovery of any similarities with other "rulebooks" as an exercise for the reader.