This is a list of other applications that can extend BibDesk's functionality. These applications are written by BibDesk users; for further discussion or to announce that you have posted a new application here, use the BibDesk-users mailing list.
Other Cocoa applications can access BibDesk through Distributed Objects in BibDesk 1.3.0. Include the Completion Server Protocol header file in your applications source code to allow fetching completions from the BibDesk server.
BibDesk searches the citekey, author/editor, title, and keywords for the given search term, so the list of matches can be fairly long. However, it's also fast, and has the advantage of BibDesk's parsing and processing beforehand. The objects provided by the completion protocol are KVC-compliant for (at least) the keys citeKey, title, numberOfNames, sortableName, lastName, and year. All values are NSStrings except the year and numberOfNames, which are NSNumbers.
A functional example program that provides a list of completion terms in TextMate is available as binary (Completion.zip) or source code (BibDeskTMCompletionsSource.zip). It also has the capability of recursively searching for TeX files based on passed-in arguments, parsing them for bibliography commands and automatically opening the files in BibDesk. After building the list of citations, it is dumped to standard output as an XML property list for display in TextMate.
Script groups can be used to automatically download citations from an RSS feed, for example from PubMed's RSS feeds. What you need is a utility that reads the RSS feed and converts it to BibTeX. RSSToBibTeX is a utility that can do this. This source code for this utility is available. It also contains the binaries. You can add your custom parsing to this code as appropriate to get proper bibtex.
To use it, save the RSSToBibTeX binary, add a new search group, set the script path to the path to this utility, an set the arguments to one or more RSS feed URLs. Add "--pubmed" as the first argument if the feed contains PubMed style authors (like in "Lastname FM").