Do you like Arabians? No seriously do you REALLY like Arabians?!? In that case I have the e-mail/forum based horse sim game for you! Ignore the references for 2006 on the front page, it really is active and up-to-date. Although the game does have all sorts of different breeds of horses (Marwari anyone?) The Arabian fans have taken over and have done a marvelous job at promoting the breed, you can easily find all flavors of Arabians in the game. (My favorite is watermelon....*ducks*). But seriously, Egyptians, Spanish, Russian, Polish, (haven't seen Persian yet but might be in there.), Domestic (of course), etc Arabians are very popular in the game. (Shagya Arabians are a separate breed btw). You can find all sorts of different half-Arabians as well.
The members are very friendly and are quick to help you out. The show system is a bit unique, and takes a bit of time to get it down right. ISG (Impulsion Sim Game) also has a very nice automated banking system which is quick to learn and easy to use. The horse registry is up-dated almost instantly which is lovely. Another unique aspect of ISG is that it is also a dog sim game and although the dogs are a smaller contingency they do have an active show scene!
If you're like me, when you join a new game you automatically gravitate to the humane society to see what equines are kicking back in their pastures waiting to be adopted. ISG doesn't have any disappointment there, many different breeds from the usual Arabians, TBs, stock horses, WBs, to other more unique breeds such as Marwaris, Swedish Warmbloods, New Forest Ponies, Dales Ponies, Knabstrups, Salernos, Welshes of all sorts, Irish Draughts, Hackneys, Fjords, Miniature Horses, Gypsy Vanners, Falabellas, Peruvian Pasos, etc, etc, etc. Most of them have show records, quite a few of them have titles in the game once you do the research on their show records.
Into the racing scene? ISG has an incredible competitive racing circuit, and there's chances to make alot of money by racing a few horses. The show scene is also extremely competitive and titles are fairly easy to obtain.
The downside is that the color of the font of the main page can be hard to read (light blue with a white background), however it doesn't distract playing that much. Lots of support in this game and a friendly atmosphere. It is for mature players (not a kiddie game) and can be alot of fun!
This is a fairly unique type of game, the typical e-mail/forum based sim horse game with some twists, some things are automated, some incredible PHP coding, and a supportive community makes ISG worth exploring! :)