Originally posted as an answer to Which NoSQL Database would be a good backend for a location-based app?
As mentioned before MongoDB and CouchDB both have geospatial support. Apache Solr and Elasticsearch are search engines which can double as a NoSQL data store.
One option is to use a traditional database (or NoSQL datastore) with Elasticsearch or Solr as an external search index. Elasticsearch does a slightly better job of doing high volumes of real-time updates. Elasticsearch supports what are called rivers. Basically, rivers are a way to update Elasticsearch in real-time. They have rivers for RSS, Twitter, Mongo, and Couch.