OmniSky and YadaYada include an Email Application from the same 3rd party developer. It is "server-side optimized" which means the email server chews up the emails as much as it can, which means faster email retrieval for you.   

During receiving of email, YadaYada's Email app offers a plethora of information including IP Addresses, status, number of mails to download, etc. OmniSky's is less verbose,  showing only the number of emails on the server, and the email being currently downloaded. Both applications offer multiple mailboxes for multiple POP3 servers, and email sorting into separate folders.