Grubbin'

This requires the OAuth Gem

# sudo gem install oauth

Add your route and create the Foursquare auth controller

map.resources :foursquare_auth

class FoursquareAuthController .> ApplicationController
  before_filter :load_consumer, :except => :destroy
  
  def index
    if session[:foursquare_request_token] && params[:oauth_token]
      request_token = OAuth::RequestToken.new(@consumer, session[:foursquare_request_token], session[:foursquare_request_secret])
      @access_token = request_token.get_access_token(:oauth_verifier => params[:oauth_token])
      current_person.update_attributes(:foursquare_oauth_token => @access_token.token, :foursquare_oauth_secret => @access_token.secret)
      flash[:notice] = "Foursquare! Yay!"
      redirect_to edit_person_path(current_person)
    else
      redirect_to edit_person_path(current_person)
    end
  end
  
  def create

    request_token = @consumer.get_request_token(:oauth_callback => foursquare_auth_index_url)
    
    session[:foursquare_request_token]  = request_token.token
    session[:foursquare_request_secret] = request_token.secret

    redirect_to request_token.authorize_url
    
  end
  
  def destroy
    current_person.update_attributes(:foursquare_oauth_token => nil, :foursquare_oauth_secret => nil)
    respond_to do |format|
      format.js
    end
  end
  
private

  def load_consumer
    @consumer = OAuth::Consumer.new(
      FOURSQUARE_OAUTH_KEY, 
      FOURSQUARE_OAUTH_SECRET, 
      {:site => 'http://foursquare.com'}
    )
  end
end

The Foursquare API documentation is a little hard to filter through. Here are a few helpers I created using the OAuth Gem and Ruby’s JSON implementation

module FoursquareHelpers
  require "oauth"
  require 'json'
  
  def foursquare_user_details
    create_access_token
    user_info = @access_token.get("http://api.foursquare.com/v1/user.json")
    JSON.parse(user_info.body)
  end
  
  def venue_search(query, lat, lng)
    create_access_token
    results = @access_token.get("http://api.foursquare.com/v1/venues.json?q=#{URI.escape(query)}&l=1&geolat=#{lat}&geolong=#{lng}")
    response = JSON.parse(results.body)
  end
  
  def checkin(options)
    create_access_token
    response = @access_token.post("http://api.foursquare.com/v1/checkin.json", options)
    response = JSON.parse(response.body)
  end
  
  def tip(options)
    create_access_token
    response = @access_token.post("http://api.foursquare.com/v1/addtip", options)
  end
  
private

  def create_access_token
    load_consumer
    @access_token = OAuth::AccessToken.new(@consumer, current_person.foursquare_oauth_token, current_person.foursquare_oauth_secret)
  end

  def load_consumer
    @consumer = OAuth::Consumer.new(
      FOURSQUARE_OAUTH_KEY, 
      FOURSQUARE_OAUTH_SECRET, 
      {:site => 'http://foursquare.com'}
    )
  end
  
end

1. Twitter
2. Foursquare
3. Foodspotting
4. TextMate
5. Github
6. Slicehost
7. Skitch
8. GMail
9. Netflix
10. iPhone 3GS
11. Photoshop
12. XCode
13. Google Calendar
14. Google Apps
15. SMS
16. Google Maps