Any good Exchange clients to replace Outlook?

Exchange provides IMAP access to a nice client, Mozilla Thunderbird. It even has a calendar plugin, lightning (not directly usable with exchange).

I think you can use just about any mail clients to connect to Exchange and utilize POP3 or IMAP, but I don't know if you would get the full array of Exchange features.

You can connect to Exchange using POP and IMAP, so therefore you can use any mail client. I use Apple Mail on my Mac personally and still use Outlook on Windows, but I also use Thunderbird on occasion.

If you want something completely free and have access to Exchange from the outside you can also use Outlook Web Access.