Who knows the most about the Product Category Page requirements?
Who is it again that is handling the monetate integration?
Who are we supposed to email about booking a conference room at the client site?
Of course these questions aren't that surprising now that we've grown as a team from a handful of collocated folks to a large team in over 5 cities on 2 continents. So we found ourselves having to implement what we called an "owner board," or as I've titled this post a Subject Matter Expert (SME) Tracker.
The concept is really simple - list out who is the best person to go to for each topic (or functional area, screen, tool, technology, etc.) along with a secondary who will cover for them if that person is unavailable.
An alternative approach more appropriate for software development lists each screen or component out, along with an owner for each of the major workstreams to complete the project - in my example this is requirements, UX, technical design, code, and QA, but you should customize this to fit your need.
Of course if you're on a bigger project, hopefully someone has you using collaboration software like a wiki or Atlassian's Confluence. In which case you could just implement a table similar to mine as a page, and link contact info there.
(If not you might want to start looking for another project, and soon.)