The Voucherify Java SDK by Rspective offers a coupon / voucher platform that can be integrated to existing Java applications. The current version requires Java 6+. Use cases: promo codes, loyalty coupons, vouchers and gifts, mobile apps
Blippy and Swipely both launched fairly recently with the hopes of making spending a social experience. Both services are very similar in that they both allow you to connect your bank and credit card info, as well as other accounts like iTunes and Amazon. After you've set everything up, as you start spending, you have the option to share these purchases with everyone. And now you can extend that sharing with the Blippy API.
Although you may not realize it on the surface, DevHub, the free site builder and hosting platform, is effectively a very sophisticated mashup using over 40 different external APIs. The Seattle-based startup, now with 10,000 site publishers who've built over 100,000 sites, have recently launched a major upgrade with new site editing tools, more content (API) partners, and new monetization tools. Their core offering takes data from APIs and other content sources as a way for niche publishers quickly create content-rich sites along with built-in monetization options: