Other Mearas?

[Firefoot]

Yes, only the Rohirrim had Mearas. The first was Felaróf, who was Eorl's horse. Eorl's father was trying to ride Felaróf and died when he was thrown, so Eorl demanded that Felaróf allow him to ride him as weregild. The Mearas were Felaróf's descendants. Until Gandalf, they would allow no others than the Kings of the Mark and their sons to ride them. Therefore, Snowmane was one of the Mearas, but Éomer's horse Firefoot (that's me ) wasn't. They were long-lived, living as long as men, and very valiant and strong.

And as to your second question, the answer is in Aragorn, Legolas, and Gimli's first conversation with Éomer:

"Then you do not pay tribute to Sauron?" asked Gimli.
"We do not and we never have," said Éomer with a flash in his eyes. "though it comes to my ears that that lie has been told. Some years ago the Lord of the Black Land wished to purchase horses of us at great price, but we refused him, for he puts beasts to evil use. Then he sent plundering Orcs, and thy carry off what they can, choosing always the black horses: few of these now are left. For that reason our feud with the Orcs is bitter."

[Orcrist]

i'm guessing you have read all the tolkien books alot firefoot. am i right

[Finwe]

Generally speaking, Orcrist, it's often a rather intelligent choice to read all of the books.

Since only the Kings of Rohan (and most likely their very near kin) were allowed to ride the Mearas, there had to have been more than one. Most likely Firefoot and Windfola (Eomer's horse and Eowyn's horse, respectively) were Mearas, or had some Mearas blood in them. Snowmane, Theoden's horse, and his mother, Lightfoot, were most likely Mearas. And, of course, Shadowfax was one of the Mearas. Already you have five names, and there were most likely quite a few more. Otherwise, they couldn't have maintained a viable, healthy breeding population. Too much inbreeding would have weakened the horses.

[Mariska Greenleaf]

the most famous mearas other than shadowfax, is Eorl the youngs horse, Frealof (i think)

You mean Felaróf (=very valiant, or very strong). If I'm not mistaken, he was like the ancestor for all other mearas.

[Roccotari Eldandil]

Mariska, I think that somewhere in the books (I don't know where--don't have them with me) it says that the Rohirrim know or believe that Orome's horse (Nahar?)was the foundation sire of the Mearas.

[Mariska Greenleaf]

Well, the horse Nahar was without a doubt one of the most powerful and exceptional horses ever described in ME, but I cannot find any reference that this would be the ancestor of all Mearas, well at least not in those words.
Oromë and his steed were known to the horse-loving people of Rohan, who claimed that the Mearas had ancestors brought out of the west by Oromë himself.
So, maybe you could make the conclusion that Nahar was the ancestor, but

Felaróf was a very remarkable horse indeed. It is even recorded that he could understand the speech of Men. He gave rise in turn to a race of wonderful horses, the Mearas, who according to tradition could only be ridden by the Lords of the Mark, Eorl's descendants. It was from this line that Gandalf's horse Shadowfax came, making him a descendant of Felaróf himself.

(The Encyclopedia of Arda)

Maybe there are other sources who can give some more information?

[Silmiel of Imladris]

After reading the posts am I right is assuming that the Mearas is a blood line that has been kept very pure over time. This still goes on today where a horse of a certain blood is worth more. The better the blood line the better the horse is something I don't believe in for a mixed breed is just as good. Just look at Hildalgo.