My husband is an equine artist, can't post a link for fear of a wrist slap from tfc but Google mark Langley. He's very good, you may have seen his work at burghley or your horse live.
The society of Equestrian artists might be a good starting point for your search.
Also worth checking out are Wendy Darker, Bridget Anne Smart, Mary Herbert.
Have a good look at lots and see which style you like, and check that they can get a good likeness, some are better at this than others. My husband has had people recognise the animals in his pictures without knowing that he has done a picture of them, for example we were at burghley and someone spotted a horse that they had owned 10 years ago who mark had done a picture for a subsequent owner. He has. Also had people recognise their friends horse or their instructors horse in one of his pictures.
My horses feature on her web site she has done 5 pictures for me
also been to crufts and done the whiskers calender and others http://www.petportraits.freeserve.co.uk/
Thank you Jade, and Katt! Annoyingly my website isn't working for Firefox users at the moment, some server issue with the provider apparently it should work on other browsers though.
As Katt said, The Society of Equestrian Artists is a good place to start- there are so many incredible equine artists out there, you are bound to find someone to suit your taste and budget!
There is a big exhibition of equestrian art on in London at the start of August- great opportunity to see who and what is out there, lots and lots of artists are exhibiting and most take on commissioned work. Some info on this thread.
Thanks so much everyone. I want to get some done of my boys but also for my best friend so need to get some sneaky pics of her boy and I can sort it out now. Thanks for the pics too
Michelle McCullagh http://www.mccullagh.co.uk/ did a fantastic painting of my old mare, see my avatar. It really captured her, it's like having her looking down at us in the sitting room!