Compaact is one of the newest AAC encoders. Like Nero AAC, compaact is not free, however it does offer an impressive feature set. Roberto Amorim's last AAC test showed that at 128kbps, Compaact! is tied with both the FAAC and Coding Technologies (Real) encoders. Compaact! features both the LC and Main Object Types, CBR, VBR, Multichannel high resolution (24bit/96kHz) encoding, and command line support.
For portable encoding, try -q5 to -q6. For music archive purposes, try -q7 to -q8.