Authenticating user over the internet

[KY]

Hi,
I am using custom authentication using SOAP headers to authenticate users of
a web service. I cannot use windows authentication as our client
applications need not in the same domain as that of server. Also, I don't
want to use WSE. I am sending user name and password in the SOAP header in
clear text. But I don't want to send username and password in cleartext
form. What is the best way to send username and password over the internet?
Thanks,
Kalyani