ARB A software environment for sequence data
SILVA 16S rRNA database and online analysis tools; ARB compatible
The Ribosomal Database Project (RDP) 16S rRNA database and online analysis tools
Greengenes 16S rRNA database and ARB compatible online-workbench
'The All-Species Living Tree' Project Curated rRNA datasets and trees including all sequenced type strains
EzTaxon 16S rRNA gene sequences of type strains of validly published species
rrndb rRNA Operon Number Database
CRW The Comparative RNA Web Site
The RNA World Website Collection of links to RNA-related information