There are a couple new TechNet articles on customizing Outlook Web Access. These are two months old now, but given that I haven't posted in some four months, I'll consider them "new". In any case, they deal with creating custom UI themes and changing the appearance of the logon page. Sometimes our development team is forwarded screenshots of the OWA UI after it's been changed by customers and many of them are really fantastic looking. If you're interested in giving OWA a look that is customized for your org you should have a look here:
Thanks goes out to Don Mace for his work with these!