I've had but no longer have a peacoat. I got mine while in a maritime academy, when it was part of the uniform. Simply put, a fashion or designed anything seem to me to be a little effeminate, while a classic peacoat something for a sailor. I'd recommend one that was a little roomy. As far as brands, the coats we had never had a brand, as far as I recall. I'd think that the best way to get a decently inexpensive coat would be to buy from someone selling surplus. In which case, you might not know the brand. However, the real article is likely to be warmer because it is likely to be made with heavier wool.

See:

http://en.wikipedia.org/wiki/Pea_coat

http://www.armynavysuperstores.com/peacoat.htm