The best replacement for d5100 is d3200.

The best alternatives to d5100 are rated as following:
★★★★★  d3200
★★★★  d5200
★★★  d90
★★★  t3i
★★★  d7000
★★★  d3100
★★  canon t3i
★  nikon d3200
★  t4i
★  d7100
★  d5300
★  600d
★  canon 600d
★  t5i
★  d3300
★  nikon d5200
★  d600
★  d3200 for beginners
★  60d
★  d300
  sony a55
  d5000
  550d
  nikon d90
  rebel t3i
  d80
  nikon d3100
  canon 60d
  d40
  nikon d7000
  canon 650d
  canon rebel
  t2i

Your alternative for d5100 is not listed? Suggest!
Speaking about d5100, one probably shouldn't forget about 35mm 1.8.

Other search terms related to d5100 and their ratings are:
★★★★★ 35mm 1.8
★★★★★ sb 700
★★ external flash
★★ 55-300
★★ 18 200
★ 70-300mm
sigma 150 500mm
You have in mind a companion for d5100 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of d5100 in all years. Click on graph for more.
d5100
d3200
d5200