Clustal: Multiple Sequence Alignment
Multiple alignment of nucleic acid and protein sequences
Clustal Omega
Latest version of Clustal - fast and scalable (can align hundreds of thousands of sequences in hours), greater accuracy due to new HMM alignment engine
Command line/web server only (GUI public beta available soon)
ClustalW/ClustalX
"Classic Clustal"
GUI (ClustalX), command line (ClustalW), web server versions available