[Boromir88]

Even if the Eagles were deployed to keep the Nazgul out of sight, it may have helped the soldiers of Gondor.~Mansun

I agree, and sorry for the bit of confusion...I didn't mean that the Eagles would not have been useful in the battle, just that for the reasons Legate gave, the Eagles could not have helped. As they were quite a distance away, Gandalf could not have contacted them (the reason Gwaihir went to Orthanc was because Gandalf told Radagast to get in touch with his bird friends to act as messengers - so Gwaihir agreed to serve as a messenger). And, even if Gwaihir knew a large battle was brewing in Gondor that didn't mean he was obligated to go help.

Let's remember too that at the Black Gate the Witch-King wasn't around (Eowyn and Merry made sure he wasn't a problem ). The Nazgul were much stronger when all nine were gathered together, and they were with their captain.

The battles fought in the North were of far less importance to Middle Earth than the survival of Minas Tirith.~Mansun

I disagree, while I agree with Raynor that Gondor was Sauron's strongest and most hated enemy, and had Minas Tirith fallen to Sauron that would make Frodo's mission far more difficult, the other smaller battles were arguably just as important (not to the fate of Frodo's quest, but to 'home' that he returned to). Especially the Dwarves, having booted out Smaug reclaiming Erebor, and their allies the Men of Dale holding off the Easterling force:

'Yet things might have gone far otherwise and far worse. When you think of the great Battle of the Pelennor, do not forget the battles in Dale and the valour of Durin's Folk. Think of what might have been. Dragon-fire and savage swords in Eriador, night in Rivendell. There might be no Queen in Gondor. We might now hope to return from the victory here only to ruin and ash. But that has been averted - because I met Thorin Oakenshield one evening on the edge of spring in Bree. A chance-meeting, as we say in Middle-earth.'~Appendix A: Durin's Folk

So technically, the Eagles arrived only to pick up Frodo and Sam.~Legate

That's a great find. I always wondered why the Eagles showed up at the Black Gate, I mean they seemed to have joined in the fight and then Gandalf 'oh since you're here Gwaihir would you mind going to pick up Frodo?' But I'm reminded of the several Letters where Tolkien comments about Eru intervening to spare Frodo. That since Frodo had shown pity to Gollum, Eru gave Frodo his own salvation and relieved him from the burden of the Ring. However, than we have the problem of...ok Ring destroyed, but Frodo and Sam are still stuck in Mordor...ah wait, in come's Manwe's eagles, ok Frodo and Sam are back. Now thinking about Eru's involvement in destroying the Ring, perhaps this coincides with the Eagles arrival at the Black Gates, not necessarily to join in the fight but to bring Frodo and Sam out of Mordor.