We've got about 500GB of geospatial data we'd like to "web-enable" to various degrees and OpenGeo Suite seems like a good route to go down given our circumstances. We can sort out a server (probably VPS) for a good price, but storing all that data locally on the same server will bump up the price considerably. So is it possible to have the VPS running the OpenGeo Suite applications, while the data is stored elsewhere (e.g., on S3)?
While there is no direct support for S3 you could use something like s3fs to build a file system on top of s3 and store your data there. However depending on the type of data you are serving most likely the performance won't be acceptable and you'll be better off using EBS.
Also Amazon just added PostgreSQL/PostGIS support for RDS which is a great option for folks now that need to store large amounts of vector data.