DreamHost is currently beta-testing RoundCube as a new webmail client at roundcube.dreamhost.com.
RoundCube is a modern browser-based webmail client with an application-like user interface (kind of like Gmail). The use of AJAX makes tasks like folder manipulation, message searching and spell checking a lot easier.
We first wrote about RoundCube about 2 years ago, and we know that a replacement for SquirrelMail has been high on the Suggestions List.
You can give DreamHost feedback in the forums.