iTunes does display the BPM of a song in your library if that information is lurking in the metadata of the song file. Only about 50 of my 2000 songs have that information, so I wouldn't expect much. I only have 1 song that lists itself in the neighborhood of 145PM and that is Level, by the Raconteurs, at 146 BPM. (Some of the BPM listings I find rather suspect - according to this, the entirety of Beethoven's 2nd crawls along at 36 BPM.) I have no way of telling how correct that tempo is, but it sounds about right.
Pre-Post Edit: Not expecting to find anything, I went ahead and typed up the above. And then I found this
website, which makes the above rather pointless. Anyways, that should get you started
EDIT: I haven't used it, but this
piece of software looks like it would be useful for determining the BPM of songs you already have.