http://www.palm.com/us/software/chatteremail/

This application turns your Treo/Centro into a Blackberry with support for push IMAP. I find this feature rather scary though.

What is useful for me though is the summary folders feature, that allows you to select several folders from multiple accounts and display it in one virtual inbox grouped by day, sorted by time and color coded based on your settings.

This helps me with quickly getting an overview of emails, and then schedule and organise emails that have tasks. Then while there, quickly file or delete emails.

Related: Email Manages You!