Free - try CalypsoMail click here
Pegasus - pmail.com
Foxmail click here
Pay - Becky from Rimarts.co.jp - my favourite and the one I used for the last 7 years or so.
The Bat click here
There are lots out there; Incredimail is perhaps the most gimmicky of them. Pegaus is an old one but very good. The Bat has its fans too. Calypso was shareware till a couple of years ago.