I was rather proud of this one. Really because it's not a terribly meaningful amount of money, but a fun optimization nonetheless.
I live in NYC, and an unlimited metrocard costs $121/month. The most you can contribute to a commuter benefit program with pre-tax money from your paycheck is $255/month. That means $134 of potential pre-tax money per month was being taxed, and my marginal rate is pretty high: ~40% between city, state, and federal taxes.
Most employers will provide the commuter benefit in the form of a debit card that will only work at transit providers. I can capture some of the excess through normal usage: Though I might only need $121 for my metrocard, I might occasionally take a Megabus to DC or the Long Island Railroad out to Easthampton for the day.
But now both uberPOOL and Via accept these transit debit cards. This by itself isn't useful, as paying for a shared ride is still more expensive than using an already-paid-for unlimited subway card. But at my previous employer I'd have to travel 2-3 times per year. In those cases I'd take Via/Uber to the airport, pay with my transit card, and get reimbursed for the expense by my employer. Voila! My pre-tax transit money is now cash.
Though most expenses would go on my corporate card, it really wasn't hard to get reimbursed at my previous employer. At my new employer I'm not sure how to expense things without my corporate card yet, but they're sending me to London in a few weeks, so I intend to find out.