This depends on [bibout](http://snipplr.com/view/19515/bibout/). In TextMate, set $TM_LATEX_BIB to point to your bibtex file, and create a Preference file in your markdown (or pandoc) bundle, containing the first line of the snippet. Create another Preference file containing the second line of the snippet. The first enables autocompletion of citations; the second enables autocompletion of bibliographic entries.

{	completionCommand = 'bibout --bib $TM_LATEX_BIB --cite $TM_CURRENT_WORD'; }
{	completionCommand = 'bibout --bib $TM_LATEX_BIB --bibliography $TM_CURRENT_WORD'; }