Nokia Messaging for 5th Edition touch screen smartphones (that means the Nokia 5800 XpressMusic) is now available as a beta, with final release still expected this May. Nokia Messaging is head and shoulders above the built-in email application (we loved it on our Nokia E71) and it supports HTML email, notifications and more. Certainly it's well worth a look if you have a 5800 and don't mind playing with beta software.
You can learn more about Nokia Messaging here: http://email.nokia.com
You can download the beta client for S60 5th Edition here: http://betalabs.nokia.com/betas/view/nokia-messaging-s60-5th-edition