Champion the Wonder Horse!
And here's a Houyhnhnm 9th level monk, using the previous version of Flurry of Blows and Unusual Physique. I haven't bothered including the detailed writeups of its Monk and Houyhnhnm Special Attacks & Qualities.
Note that it flurries as a 13th level Monk (9th level Monk +4 levels from the Houyhnhnm's flurry of blows SA for a base of +9/+9/+9/+4), and if it uses its amulet of magic fang it gets +1 enhancement to attack and damage for Flurry of blows +14/+14/+14/+9 (2d8+5/19-20). Said amulet is a custom magic item that follows the SRD rules.
Houyhnhnm Champion
9th level Monk
Large Magical Beast
Hit Dice: 3d10+9d8+48 (105 hp)
Initiative: +4
Speed: 90 ft. (18 squares)
Armor Class: 24 (-1 size, +4 Dex, +4 natural, +1 armour, +5 monk, +1 deflection), touch 19, flat-footed 20
Base Attack/Grapple: +9/+21
Attack: Unarmed strike +13 melee (2d8+4/19-20)
Full Attack: Flurry of blows +13/+13/+13/+8 (2d8+4/19-20)
Space/Reach: 10 ft./5 ft.
Special Attacks: Brave, flurry of blows, ki strike (magic), stunning fist
Special Qualities: Brave, improved evasion, low-light vision, purity of body [immunity to natural diseases], scent, slow fall (40 ft.), still mind [+2 save vs Enchantment], unusual physique, wholeness of body [heal 18 hp/day to self]
Saves: Fort +14, Ref +14, Will +14 (+16 vs. enchantment or fear)
Abilities: Str 19, Dex 18, Con 18, Int 14, Wis 18, Cha 10
Skills: Autohypnosis +8, Climb +13, Escape Artist +10, Hide +11, Jump +32, Listen +14, Move Silently +11, Spot +14, Survival +8, Swim +8, Tumble +13
Feats: Deflect ArrowsB, Endurance, Improved Critical (unarmed strike), Improved Grapple, Improved TripB, Iron Will, Stunning FistB, Weapon Focus (unarmed strike)
Challenge Rating: 11
Alignment: Lawful neutral
Advancement: By character class
Level Adjustment: +2
Magic items: +1 bracers of armour, +1 ring of protection, +1 amulet of natural armour, +1 cloak or resistance, amulet of magic fang (3/day, use-activated, caster level 1)