The best replacement for ipod nano is ipod touch.

The best alternatives to ipod nano are rated as following:
★★★★★  ipod touch
★★★★  ipod classic
★★★  touch
★★★  shuffle
★★★  classic
★★  zune
★★  ipod shuffle
★★  ipod
★  sony walkman
★  ipod mini
★  mini
★  ipod video
★  mp3 player
  creative zen
  sansa clip
  sandisk sansa
  zune hd
  touch which is better
  ipod touch 5th gen
  sansa fuze
  creative zen v plus
  nike watch
  zen micro
  mp3 players
  flip video
  zune 8gb

Your alternative for ipod nano is not listed? Suggest!
Speaking about ipod nano, one probably shouldn't forget about nike+.

Other search terms related to ipod nano and their ratings are:

★★★★★ nike+
★★★ docking station
You have in mind a companion for ipod nano and it is not yet here? Propose!

Google Trends

Scale is based on the average worldwide traffic of ipod nano in all years. Click on graph for more.
ipod nano
ipod touch
ipod classic