If you are using Windows Server 2008, you can use the built-in fax server role:
Win 2008 Fax Server There is similar functionality in Windows Server 2003 (and even with Win Server 2000) but it doesn't do routing of received faxes like Win 2008 does - instead all received faxes arrive in one Exchange/Outlook mailbox.
I have installed the FaxFinder product, works as advertised. Bonus: in my experience Multitech fax support has been A+.
Don't have experience with Faxtalk, but for the price it's worth a look. I've had experience with Brooktrout and MainPine multiline fax boards with no complaints.