Gmail is simply awesome! You get tons of storage, instead of deleting messages you have the option to archive them and google-search them later (including searching for all messages from a given e-mail address), send attachments up to 20MB.
Plus, there are other features:
Google chat--an integrated instant messenger client that lets you talk to anyone on Gmail or with an AIM account.
Google calendar--manage your calendar from any PC on the web, print out hard-copy calendars, and let frends and family see your calendar if you wish, others can share calendars with you too.