https://github.com/loopj/jquery-tokeninput
I just had a go at this one and it was really easy to implement using an asp.net page to output the JSON (from the search params)
Then theres just a few lines of Javascript you need to create it (and the settings)
$(document).ready(function() {
$("#Users").tokenInput("../Services/Job/UnassignedUsers.aspx?p=<%= projectID %>&j=<%= jobID %>", {
hintText: "Begin typing the user name of the person you wish to assign.",
noResultsText: "No results",
searchingText: "Searching..."
});
});