'Entrenchment' was scheduled for release tomorrow but has been pushed back to adapt some more user feedback into the micro-expansion.
It adds starbases to Ironclad Games' Sins of a Solar Empire, a real-time 4X space strategy game. It's hotly sought after by the community with it originally intended to release in '08.
It's only available through Stardock's Impulse digital distribution service with the add-on priced at $10. A further micro-transaction is planned that will eventually upgrade the games diplomacy system, which is rather lacking compared to the rest being quite stellar.