The best replacement for imgur is photobucket.

The best alternatives to imgur are rated as following:
★★★★★  photobucket
★★★★  flickr
★★★  tinypic
★★★  imageshack
★★  reddit
★★  9gag
★★  tumblr
★  minus
★  imager
  4chan

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

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



Google Trends

Scale is based on the average worldwide traffic of imgur in all years. Click on graph for more.
imgur
photobucket
flickr