The ones I use a lot are mainly this
, but also this
, and this
, and surprisingly, some MLP-themed songs- this
. That's not to mention Rujio and Boney's songs, which are all pretty darn good. All of the above songs seem to work pretty well for me. Of course, I just really like those songs, especially the instrumental ones, so they're kind of excuses for me to listen to them while doing other things- which is quite alright, in my book.
Also, I read somewhere that good productivity songs are also songs that you would work out to, so I suppose that some of mine would be this
, and pretty much anything off of the OSTs of Castlevania: Circle of the Moon and Harmony of Discord. Then again, I listen to any random song on my music library while working out, and it's extremely varied to the point of not having any common themes or genres, so that's probably not ideal.