@Satsuki:
Who was the Zaraki clone? Nnoitora?
Yep, it's him. Of course he's got his differences from Zaraki but still with all this strenght obsession he pretty much is the Espada counterpart of Kenpachi. Actually everybody Ichigo fought is a Soul Society clone.
1. Dordoni = Ikkaku
Somebody that at first sight strikes as random Arrancar but then turns out to be a former Espada. And after his fight he gives Ichigo even some advice for his upcoming confrontations. Now for Ikkaku.
As somebody who's not even Vice-Captain he also struck as random Shinigami at first but in the end he turned out to be 3rd seat and later on with his Bankai that he could actually even fit a Captains rank. And he also gave Ichigo some advice for upcoming confrontations after he lost to him.
2. Grimmjow = Renji
The first Espada Ichigo started a personal feud with in the real world. Even though he came for Orihime Ichigo just had a score to settle with Grimmjow in Hueco Mundo. This is the exact same thing that happened back then at Soul Society when his priority was to rescue Rukia. It wouldn't have worked out well if he wouldn't have settled a score with Renji.
3. Noitra = Kenpachi
Noitra was nobody Ichigo wanted to fight but simply was confronted with against his own will. Same thing with Zaraki. The only difference in the fight is that Ichigo won against Zaraki while he lost against Noitra (which makes sense considering that he had no time to recover from his fight against Grimmjow).
4. Ulquiorra = Byakuya
With all big (and boring) talk Ulquiorra strikes more as the chain that is holding Orihime prisoner then anything else in Hueco Mundo. At least to Ichigo which is why defeating him means rescueing Inoue for sure (even though if Aizen is the top boss). This is the same as at Soul Society where Byakuya seemed to be the ultimate obstacle that needs to be defeated to rescue Rukia (even though Yamamoto is Byakuya's superior).
The funny thing is not only that these guys are the exact clones of them, but that Ichigo's real fights with them even follow the exact same order as in Soul Society. Yes, he confronted Ulqiuorra before Grimmjow but to Shonen standards that doesn't count as the real, final fight.
If there's anything that's different from back then, then it is that the first Espada team that came to Karakura Town was Ulquiorra and Yammy instead of Ulquiorra and Grimmjow which would have been the counterpart of Byakuya's and Renji's comming. But perhaps Kubo went that route because it could have been too obvious. OR perhaps he simply didn't plan that far ahead. =/