Very good app CallRecorder I have in Nokia E72, I found it in Symbian platform by SmartphoneWare. But now I'm using Lumia 920 and waiting for similar app as on Symbian. Also AnsMAchine (same on Symbian) is one of very good and useful application, but not yet on WP8 .
Better rephrase it to "but no longer on WP" since the function has been disabled from the OS level in WP8 (and probably also in WP8.1)...