As of January 9, 2012, the SAO/NASA Astrophysics Data System (ADS) started indexing ASCL entries. Codes can be cited as [author], [year], [code name], ASCL [ascl ID number], for example: Nemiroff, R. J. 1999, BHSKY, ASCL 9910.006

To provide an online citation to a particular entry, you can use the ascl ID number. For the example above, typing ascl.net/9910.006 into your browser brings up the entry for BHSKY.

Edited 11/28/2012 to add:

Most citations to codes have been in the format:

author, year, in Astrophysics Source Code Library, record ascl ID

For example: Barnes, J. E., 2011, Astrophysics Source Code Library, record ascl:1102.027

Using the entire ascl ID (ascl:xxxx.xxx) in the reference enables ADS to more easily pick up the citation. It may be helpful to the reader to include the name of the code as well:

Barnes, J. E., 2011, ZENO, Astrophysics Source Code Library, record ascl:1102.027

The ascl ID number can be used to provide a link to a particular entry. For the example above, typing ascl.net/1102.027 into your browser brings up the entry for the code ZENO.