How do I avoid the server-specified security policies for my work e-mail?
First off, talk to your Exchange administrators.  See if they deliberately are setting the mobile device security settings so tightly.  I would have a discussion with them to see if they can loosen up the security settings.

If you only want email you could try K-9 from the app store.  It uses IMAP to get the mail from the server so your exchange server will have to have that turned on.