Jaikoz is an excellent id3 tagger and has helped me "save" my collection as poorly tagged songs made it difficult to find anything. The developer is rather responsive on his forums and often updates his wishlist and buglist to let you know where his priorities are at the moment.

In addition to cleaning up tags, it adds album art and lyrics, and can help dedupe your collection. Yes it can be a bit slow, but some of that slowness is the limitations of the MusicDNS servers that it uses to help identify songs. (they have a throttled limit of 1 song/second plus, the server is often busy causing Jaikoz to retry a few times to ensure it gets the information)

I concede that it can be difficult to load entire collections at once, especially as people's collections get so huge. (we are now what 11 years into the mp3 revolution?) However, it has improved and should keep improving (I can now get about 15K-20K loaded at once).

One of the best $22 I ever spent.