Yeah, I have to wonder if there's an exclusivity agreement with the Oracle licensing in RDS that requires that MySQL and Oracle be the only options for linux databases.

Seconded, if it includes PostGIS. I'd love to have something in the cloud with operations over more than just points for small hobby projects.

I stumbled upon this http://enterprisedb.com/cloud-database recently which may be of interest. Haven't tried it myself though.

Heroku offers a hosted and managed Postgres (including the option of PostGIS 1.5) that's on AWS: https://postgres.heroku.com/

Seconded. It's gotta be on the RDS roadmap.