Vocals - Awake...i mean...yeah, cīmon.
Guitar - SDOIT...misunderstood, glass prison, test that stumped them all, war inside my head...and the list goes on.
Bass - Systematic Chaos...controversial, but the bass has a very interesting function in songs like ITPOE part 2. and the intro, amongst other songs in the album, I want to give a honorable mention to FII though, its very powerful in there.
Keyboard - Octavarium...the album requires from Rudess many interesting lead sounds as well as the sole piano, it shows a good range of his sounds and techniques. Honorable mention to SDOIT, where he samples the whole orchestra in the Oasys (i think).
Drums - Train Of Though...as a more heavy album, i find the drumming to be very intense.