Gain 10% CDR when you reach level 10. Excess CDR becomes AP or AD, Adaptive.
Unsealed Spellbook on Ryze allows you to run a various number of Summoners in the mid lane (Cleanse, Ghost, etc.) depending on your matchup while still being able to swap to Teleport later in the game for more map pressure.
The stasis active from Stopwatch and Zhonya's in an incredibly component of Ryze's kit, allowing you to [R]->Stasis to get out of sticky situations.
Minion Dematerializer allows you to effectively wave-clear to match roam timing and get efficient recall timings off.
On Ryze you are able to Dematerialize->[E] and if the minion dies while your [E] is mid-air your [E] will spread as if you had killed it.
Cosmic Insight is an all-around fantastic rune choice for Ryze. The extra bit of CDR let's you pump out more DPS and the extra Summoner CDR helps keep you safe in the laning phase.
Manaflow Band synergizes well with Ryze's natural tendency to build up a massive mana pool. The missing mana refund will allow you to continue spamming in teamfights to pump out massive DPS.
Transcendence allows you to hit 30%+ CDR in the mid to late game when combined with Morello's and Zhonya's so that you're able to deal massive damage to repeated spell casts.