I have tried dozens of FREE Push Email applications on my N95 and N73, and hope to share my experiences and hear from others if there are better ones.
Emoze: It works Windows Mobile or Symbian devices. It used to require set up of a desktop agent software, now offers a solution without the PC based connector using the Emoze Global Gateway �OWA�. Also offers support for address book and calendar access. www.emoze.com
Morange: Singapore based Morange provides a Java based solution. It also offers Windows mobile version for Push Email solution. Latest version (I just tried several days ago) supports Hotmail, Yahoo, and MSN mail. Morange also Offers a plethora of features other than push email, like IM, RSS, VOIP, SMS, Social Network. www.morange.com
Flurry: Flurry is one of popular mobile email applications. Supports java enabled devices and claims that it has users in 200+ countries. Offers a free solution.www.flurry.com
Consilient: Offers solution for a variety of Java enabled and Smart phone. The free service is added supported. A list of supported devices is provided here http://www.consilient.com/help/phones/
Movamail: Movamail supports a wide range of java enabled devices and additionally offers a browser (XHTML) based client software. Like flurry they claim users in over 200 countries. Offers some nifty features like camera phone support and compression.