Most people don't know because it's not advertised to my knowledge, but there's an underground market for tax credits. Bankers tend to finance huge deals in real estate development, in part due to the developer's ability to receive tax credits from the state or feds for the development. The bank then often brokers these credits to their customers, or CPA firms and their clients. I've brokered a few nice deals for clients, and I once purchased some from a client.
They tend to sell at around $0.90-0.92/$1. The savings can be enormous. If you work closely with, or personally know any bankers or CPAs it might be worth a discussion. However, they like to sell at $100,000 increments to reduce paperwork, so you sort of need to achieve "baller" status before you have access. The credits can be carried back and forward as well though, so you can use them over multiple years. The best thing to do is buy them at year end, use them for 2015, and carry them back to 2012-2014 in January 2016. This let's you get a bunch of refunds all at once reducing the time before you realize a return on the cash outlay.