Nero just release a free command line AAC encoder. I haven't checked it out yet but it looks pretty interesting.
http://www.nero.com/nerodigital/eng/Nero_Digital_Audio.htmlFrom the link:
Nero Digital Audio Reference Quality MPEG-4 & 3GPP Audio Codec
Compression Ratios ranging from ultra high (58 CDs fit on one!) to High-End Audio (2.5:1), for absolutely perfect audiophile encodings
Crystal Clear, Award Winning Sound Quality at every compression ratio and bit rate!
Support for Embedded Album Art (Covers, Booklets, Lyrics!)
Store Entire Audio Album in a Single .mp4 File with all the Features of an Audio CD embedded inside, but at a fraction of the space!
Reference Quality MPEG-4 Audio Codec
Fully Compatible with the Latest Version of the State-of-the-art MPEG-4 Audio Standard (LC-AAC, HE-AAC and HE-AAC v2)