The best replacement for 40d is 5d.

The best alternatives to 40d are rated as following:
★★★★★  5d
★★★★★  50d
★★★★  60d
★★★  xsi
★★★  t2i
★★★  7d
★★★  d300
★★★  nikon d300
★★  t1i
★★  t3i
★  450d
★  d200
★  30d
★  d90
★  400d
★  d80
★  20d
★  nikon d200
★  canon 50d
★  xti
★  5d mark ii
★  1100d
  nikon d80
  1000d
  5d classic
  1d mark ii
  canon 5d
  550d
  500d
  30d canon
  nikon d90
  5d mkii
  rebel xsi
  7d canon
  600d
  nikon 300
  450
  k20d
  1d mark iii

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Speaking about 40d, one probably shouldn't forget about 24-105.

Other search terms related to 40d and their ratings are:
★★★★★ 24-105
★ 580ex
★ 24 105
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