from http://code.msdn.microsoft.com/Contact-Manager-Web-API-0e8e373d

ContactsController.cs

using System;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using ContactManager.Models;

namespace ContactManager.Controllers
{
	public class ContactsController : ApiController
	{
		private readonly IContactRepository repository;

		public ContactsController(IContactRepository repository)
		{
			this.repository = repository;
		}
		
		public IQueryable<Contact> Get()
		{
			return this.repository.GetAll().AsQueryable();
		}

		public HttpResponseMessage<Contact> Post(Contact contact)
		{
			var post = this.repository.Post(contact);
			var response = new HttpResponseMessage<Contact>(contact) { StatusCode = HttpStatusCode.Created };
			
			string uri = Url.Route(null, new { id = post.ContactId, controller = "Contact" });
			response.Headers.Location = new Uri(Request.RequestUri, uri);
			return response;
		}
	}
}