Tremolos, repeated notes, double octaves.
I've read some confused advice about this in this thread.
Tremolos are not played with the wrist.
The entire arm is engaged when playing a tremolo correctly, and if you attempt to play it just from the wrist and forearm, you'll NEVER get it.
Tremolos start with the upper arm and radiate down to the hand and finally the fingers.
You must first develop the sense of engaging the upper arm, and to do this, you have to sit well.
It should almost feel "sloppy" in that you want it to feel very free. Once you accomplish this... and it is a MUST... then try to feel the connection with the upper arm to the fingers.
If you can get this feeling consistently and practice it, you are 90% there!
This, BTW, is the same feeling everyone talks about when they say "playing with the arm".
Practicing fast rotation with the forearm in the air is useless, and not what you want at all!
The first mvmt of the Pathetique has excellent tremolos you can use as an exercise.
I'd avoid the Waldstein at first for learning tremolos, because being a smaller interval, one can "cheat" by NOT really engaging the upper arm. With the larger interval in the Pathetique, its really an excellent vehicle for getting the "feel" for tremolos.
In Hannon, there is a monster of a tremolo exercise which is mostly chords played as tremolos, and it is quite formidable.
Also, all Alberti-like basses are all tremolos really, as well.
And then there are trills which are really "small interval tremolos".
Trills and tremolos are literally every where in classical music, and I would say that if you can make them a main part of your technical training, they will greatly aid scales, and arpeggios (believe it or not) because they directly employ learning to play by engaging the whole arm in varying degrees.