Is there like a list of the top 20 otaku songs or something?

No.

>>16817313
aw. No otaku magazine tracks cd sells or something?

>>16817218
try the Oricon chart site itself is the only solution that I can come up with.

File: montage.jpg (571KB, 1920x1620px) Image search: [Google]

571KB, 1920x1620px

Nicovideo medleys and kumikyoku provide a view into what of what arbitrary people have figured are well-known songs, though they have a recency bias. You could also just search for 音楽 and search by views but that'll be biased even more in favor of memetic smash hits. I'll shill ニコニコ動画摩天楼 again just because I already have an image for it.

ニコニコ動画摩天楼 (2015)
https://www.youtube.com/watch?v=HzFRMRagXlg
http://dic.nicovideo.jp/v/sm27429088

Someone will probably come along shortly and say that nicovideo is awful niwaka garbage not representative of anything, but I'm sure he can give you a better answer when he does.

>>16818669
Surprising amounts of idolmaster in the anime weekly.monthly lists.