If you're a fan of PostgreSQL, you'll certainly be interested in Postgres-XL. It's a scalable database cluster based on PostgreSQL, fully ACID compliant and open sourced last month by TransLattice. The Postgres-XL home page points to a few different use cases, including large-scale data capabilities with MPP and ease of database scaling. And, of course, it's bigger:
That's two more elephants than you're used to.
PostgreSQL equipped for Big Data is an interesting prospect, though. According to the Postgres-XL overview, it can handle quite a few different workloads, such as OLTP write-intensive workloads, BI requiring MPP parallelism, key-value stores, and GIS geospatial, among others. And given that Postgres-XL is based on PostgreSQL, a lot of regular PostgreSQL apps will migrate without any need for changes, which is always nice.
You can find Postgres-XL on SourceForge if you want to give it a try.