Sure, iTunes can join tracks, but only if they're consecutive CD tracks, and you haven't imported them. This script allows you to join any two (or more) MP3 tracks (repeat: MP3 tracks only), provided that they are the same format and bitrate.
Also see Join Together, an application that will join any type of files.
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Re-associate batch of dead tracks with files from selected folder
downloaded 16m 24s ago
Re-locate files of selected tracks to new folder, preserve track meta-data
downloaded 19m 58s ago
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
downloaded 34m 8s ago
Resample selected tracks' artwork to user-set size limit
downloaded 46m 14s ago
Write size of track's artwork to chosen tag or copy tracks with artwork of certain size to playlist
downloaded 46m 54s ago
Convert selected tracks and replace them with converted versions