Who should write a recommendation letter?
Your letters should come from experts in your field who are familiar with your work.  They should be written by professors who are substantially more senior than you are, and who will be known to the people reading your applications.

A typical situation for someone applying for a first job out of graduate school would be one letter from your advisor, one letter from someone else in your dept. who is also an expert in your field, and one letter from an expert at a different school who saw you speak in a seminar or at a conference and who has read your papers.  It is not necessary, at the new-graduate level, to have had more substantial interactions with outside letter writers than their having seen you talk and read your papers.  If you can get two good outside letter writers, then do that instead, but in my experience it's common to have only one outside letter writer at this stage.  At least two of these people should be at the associate or full professor level, and all should have excellent tenure-track jobs.  For someone a few years out of Ph.D. one would expect, in addition to the Ph.D. advisor and postdoc advisor, letters from well-known experts in the field who have interacted more substantially with the applicant.