Plex Recorder is a free to try tool that works in conjunction with Skype for recording calls. It has the following advantages: can work in automatic or manual mode, automatically compressing to MP3/WMA formats, can save as WAV PCM format, record conversations either in single or dual audio track, all versions of Skype supported, doesn`t inform other side that you are recording the conversation, user-friendly interface, free for try, etc.