Like most Magic: The Gathering cards, the value of Rabanastre, Royal City depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Final Fantasy)
The other two dragons have to be in the library while Scions on the battlefield
While untapped blue mana is often regarded with suspicion, Force of Will allowing you to cast it without any mana at all has left an indelible mark on the game
Theyre plenty good if you only use them to get two of the three colors they fix for, and some decks (notably those with Landfall and Sacrifice triggers) will use them even if they only hit one of their colors
I like Honored Knight-Captain quite a bit
From these you can pick and chose as you like to make up the numbers but in reality there are only about ten Izzet cards that have seen cube play two or more times and of those only five that are into the double figures