Here's a neat little collection of fantasy mounts for your cavalier characters (or indeed anyone who is fed up walking), stemming, as the author points out, from the thought having arisen one day: Why should the only riding beasts available be horses or a camel if you're lucky.
A Cavalier is defined by his mounted status after all, and as this is a fantasy world, fantasy mounts are surely appropriate. So here we have the likes of salamanders, elk, eagles, hawks and spiders all presented rather bare bones (just the statistics you'll need to run them including the level-based advancements). The underlying concept is that these are animals that are bred and trained to be riding beasts, very likely by cavalier orders for their members, and so likely to be quite hard to obtain if you are not a cavalier of the correct order!
Inventive GMs - or even business-savvy PCs - might set up a business breeding and training a particular species as mounts, of course... indeed, I can feel an adventure idea coming on... but they are still likely to be hard to acquire and quite expensive.
Neat thoughts, ripe for expansion and incorporation into your campaign world.
(As an aside, I actually find the 'printer' version easier to read electronically than this one!)