We were one of the relatively early businesses to accept BTC as a payment option, and even though we only took a few hundred dollars worth of BTC in 2011, it boggles the mind what it would have been worth today.
And the best thing was that I didn't even spend a cent to buy the coins in the first place, but instead someone just gifted them to me on /r/Bitcoin when they were worth around 15€. One time it even fell down to 6€...
Space program? Code-breaking? Nuclear weapons? Dot-com boom? Real-estate? Search-engines? Social media? Oil? Gold-rush?