I've got 2 games with a lot of sentimental value.
The first game, a Gottlieb 2001, came from our neighbors. I was childhood friends with the kid who lived there, and the game sat in his basement. It never worked, but we would always play on it. We were either climbing all over it, or we'd sit on the glass (good thing it's tempered!), and pretend we were sitting in a racecar. One spring day, they decided to sell it, and my mom bought it for my dad, thinking he'd like to tinker with it. I'll never forget watching my neighbor's dad and my poor mother hefting that cabinet, legs attached and all, down the sidewalk and into our garage. It sat in our garage for a couple years, since my dad immediately lost interest in fixing it. I found Clay's guides and DVDs, and he and I found renewed interest to fix it. We did, and it was our first father-son project together. What a great summer that was!
Second game is Whirlwind. It's the first game (other than 2001) that I can actually remember playing. It was in an old shed at a campground we were staying at for a Boy Scout outing in the early 2000s. I've always been somewhat of an outcast, so finding a little slice of fun was a nice getaway from the daily roasts and ridicule I'd often be afflicted with. It was a really hot day, and the fan on the game was just icing on the cake. While I got multiball once or twice, I remember thinking "Wow! I'll never be able to hit that side ramp! I wonder what that does?!" The game was filled with mystique, and I loved the music. It took me years to find a copy of the game I could afford, but now that I have it, I doubt it'll ever leave the collection.