My employer doesn't offer any incentives, but I've been lucky in both this employer and my last (although I didn't commute by bike back then, I know of several people who did) in that they were flexible, had showers and lockers available (currently through the fitness center on campus; my last employer was a symphony and there were showers and lockers for the performers, but anyone could use them), and secure parking--right now it's in the form of bike racks, one of which is in a nice covered area; at my last employer the bike commuters could leave their bikes in secure stairwells that were locked to all but employees and had security cameras running all the time.

My current employer is a bit irritating in that they DON'T seem to encourage bike commuting, although there's a serious parking problem on campus. They offer incentives to people who park at a nearby mall and take a shuttle ($5 cafeteria card for every 5 round trips--not that big a deal, but I wouldn't turn down a free lunch!) but don't offer the same incentive to those of us freeing up parking space by biking.

Sarah