We are interested in seeing proposals for new books (including books based on PhD theses, provided they are of sufficient general interest). All book proposals are reviewed by experts in computational linguistics. I am happy to give informal feedback on book ideas but actual proposals should be sent to CSLI publications. For more information and contact details see the CSLI publications web site and especially the information for authors.
Software associated with books can be distributed with the book on a CD as was done with Beesley and Kartunnen's book. Alternatively it may be made downloadable via the author's own website: for instance Blackburn and Bos's book has assocociated software that can be accessed from this software download page.
The new online series (CSLI Studies in Computational Linguistics Online) should be useful for conference organisers who need quick publication.