As alternative for an Exchange client, you might wish to check out the Work Email app hacked out (by xda developers) of the Magic/MyTouch. It's free and supports: html email, signatures, folders, attachments, etc. This functionally does the job of the native Corp Email client while allowing use of the native Contacts and Corp Calendar app.
In addition to configuring the Work Email client, I still have my ... Menu/Accounts & sync/Corporate account set up as follows (under Account settings):
General Settings:
-Email check frequency - Automatic (Push)
-Amount to synchronize - One day
Notification settings - nothing checked
I also Calender and Contacts selected to sync
More information is available
here. Or download via UPC: