It depends a bit on what you're looking for. If you want the Rohirrim to be closer to the existing warriors, the minis mentioned before by other are great. For minis closer to the books (in the books, the Rohirrim only wore long coats of chain mail), I got a few more recommendations.
Crusader Dark Age Ranges, like the Normans:
http://www.crusaderminiatures.com/list. ... =12&page=1Excellent minis, I got some Byzantines as well and I can really recommend this company.
Musketeer Miniatures, Dark Ages, like early Saxons:
http://musketeer-miniatures.com/store.p ... ical&id=35Alternatively, the Late Romans/Anglo-Romans or the Goths, might be great!
Artizan Design, Dark Ages, like the Vikings (especially good for foot, no mounted here):
http://www.artizandesigns.com/list.php? ... 117&page=1The Carolingians might be closer to the Rohirrim in the movies for the use of scale mail, with a head swap.
Perry Miniatures, First Crusade. Lots of mounted troops, all looking great!
https://www.perry-miniatures.com/index. ... h=23_33_52I got some Muslims from the First Crusade and they look great. Amazing sculpts, great casts and great prices! I can really recommend these as well.
Ebobminiatures, Dark Age Normans:
http://www.ebobminiatures.com/products/darkages.htmOnly foot models so far, but oh do they look marvelous?! I think so!
Again, I can really recomment Ebob: great sculpts, great casts and great prices.
Gripping Beast, Dark Age minis from SAGA:
http://s121252763.websitehome.co.uk/gri ... CatID=2398Especially the Normans, Carolingian Franks, and perhaps Strathclyde Welsh seem to be useful, though if you are looking for infantry, other ranges are great as well.
Like the other companies, I got some GB minis and I can really recommend also this company.