The best replacement for foursquare is yelp.

The best alternatives to foursquare are rated as following:
★★★★★  yelp
★★★★  gowalla
★★★★  facebook places
★★  facebook check in
★★  places
★★  scvngr
★  google places api
★  loopt
★  factual
★  tripadvisor
  assemblies of god
  facebook checkin
  path
  latitude
  whrrl

Your alternative for foursquare is not listed? Suggest!
Speaking about foursquare, one probably shouldn't forget about amex.

Other search terms related to foursquare and their ratings are:
★★★★★ amex
★ foursquare
You have in mind a companion for foursquare and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of foursquare in all years. Click on graph for more.
foursquare
yelp
gowalla