dBpoweramp Free Edition - CD Ripper & Audio Converter (Windows/OSX)
dBpoweramp is one of the best known programs on Windows for mainly ripping CDs to lossless (uncompressed) audio formats such as FLAC, or if you prefer, then on MP3 (compressed/lossy).
The Free Edition besides ripping CDs also offers to convert audio files in a more sophisticated way than the rest of the programs which all claim to be the "best" do.
If you want to convert music specifically to M4A (AAC), then download this file (for Windows) from their website and install. Afterwards you can convert it and it will be relatively identical to the previous lossy audio format it was on, as long as the settings are kept in a similar manner.
Here's a chart that shows the difference between Free and Reference (Paid).
The full version, for example, costs £31 for a single PC.