try songs from the game VVVVVV some of them tune in REALY well whit the rythem!
especial some of these:

for example: Pushing onward.
and my favorite: potential for everything.
these are some of my favorite tracks from VVVVVV i think it fits the game well!

EDIT:
while im at i guess i can also trow in halberd from kirby epic yarn but thats just a personal favorite ;) https://www.youtube.com/watch?v=X6pE8z4K1Gw

http://www.newgrounds.com/playlists/view/d62b3bece0125e4ab49c9662429c8833 - any of those are awesome.

I've been having a lot of fun using the Shovel Knight soundtrack.
https://virt.bandcamp.com/album/shovel-knight-original-soundtrack

Though I almost always prefer the default one, just because of the Shopkeeper. I hope they eventually let you add a second vocal track to custom music.

I just got the game and started playing it with the Beatbuddy soundtrack, It may not suit the theme all too well, but its really fun!

Though it does cost...
https://beatbuddy.bandcamp.com/

Someone recommended this song in the wiki: https://www.youtube.com/watch?v=SH6YD6XuA3g
I tested it and it fits the game sooooo much.

Super Meat Boy music, which is also another Danny B soundtrack, works wonderfully with necrodancer even though it does take a bit of hunting to get the right mix of songs per zones,

Cool, thanks for the responses everyone, I'll try them out!

https://www.youtube.com/watch?v=jigRSeRYMzA

Super Hexagon's soundtrack has been working pretty well for me. I absolutely second Bal's comment on the shopkeeper's vocal additions being amazing/missed though.

https://www.youtube.com/watch?v=Gij7h4CTJMk
looks like a bunch of kirby music works

http://lapfoxtrax.com/track/wanderlust
Even setting this to 2x Speed only accounts for 1/2 of the BPM of this track. mwa ha ha

but seriously, these are fantastic
http://lapfoxtrax.com/track/pseudotriton (2x speed)
http://lapfoxtrax.com/track/vultures (1x speed)
http://lapfoxtrax.com/track/disinfect-the-dead (2x)
http://lapfoxtrax.com/track/gunners-heaven
(I WISH we could replace boss music)

Additionally I have found a few tracks that cause the game to instantly skip the level, which means if you put it for all the levels, you skip right to the boss level w/o equipment (starts you on a trap door every time because it can't detect any beats, because variable tempo)

Thriiiiiiler ! Thriller night ! Toudoudoudoudoudou clap, toudoudoudoudoudou clap !

Barbra Streisand by Duck Sauce
Oooeeooeeooeooeoee-oo-oo, Barbra Streisand!

I just made 3 remixes of the tetris music, in different tempos with different instruments and drums, specifically to dump in this game, because video game music in a music game. anybody want them?

https://www.youtube.com/watch?v=GSck5v0V7wE This music would fit perfectly with the game.
But the beginning messes with the game's beat detection.
Somehow, you would have to cut the 30 first seconds.
This is a great track from Trash80, and it reminds me Thriller a lot. :)

I tried using some stuff from AdhesiveWombat from Youtube. It fits with the game decently, but be wary of tempo changes in a couple songs.

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