The Codon Usage Database

http://www.kazusa.or.jp/codon/

The flatfile release of GenBank is mined for coding 
sequences (CDS), and codon usage tables are generated 
for every gene. These can be searched alphabetically 
by organism. 

The Countcodon program is also available to generate a 
codon usage table from a user-provided CDS.

Recall that Nc can be calculated from codon usage tables alone.

(Codon usage tabulated from the international DNA sequence databases: status for the year 2000. Nakamura, Y., Gojobori, T. and Ikemura, T. (2000) Nucl. Acids Res. 28, 292.)