Windows only: Lengthy MP3s, like a poorly converted audiobook or an analogue to digital recording, often need to be chopped into smaller, easily managed MP3s. MP3Extractor will make short work of it.
MP3Extractor allows you to load a long MP3 file and set markers. Depending on the type of recording you are flagging those markers could be chapter stops in and audiobook, between songs on a rip of an analogue album, or other helpful demarcations.
As you set your markers you assign values to them like album, artist, and title. When you're done working your way through the recording, MP3Extractor will create a series of individual MP3 files named using the titles you gave each marked block of the original recording. With a little bit of work, your monolithic audiobook is carved into smaller and properly labelled files.
MP3Extractor is freeware, Windows only, and requires that Winamp 3.0+ be installed.