You may already know, but iConcertCal is very useful and we think it is worth another reminder. With the free plug-in, you should never again miss a show due to bungled dates or forgetfulness. Eliminating the need to thumb through magazines or surf through sites, iConcertCal scans your iTunes music folder to comprehensively detail live concerts in a well-organized and personalized calendar. Available in both Mac and PC formats, you can click on your choice to purchase tickets through the venue's website.
A similar service, Sonicliving is arguably more powerful as it is web-based and scans not only your iTunes, but your internet radio and pandora accounts as well.