Roughriders are fantastic at what they do - a great counterattack element for unbelievably cheap. An IG army doesn't really need that, you can just sacrifice and take the cc losses with fodder units. But if you want a counterattack element without investing much they are the way to go. They only get one useful charge, but who cares? Problem is there are no good models, none (except for forgeworld, at prices that would bring tears even to Shadowlords eyes). You'll have to do some big time converting, unless you fancy the incredibly ugly Attilans.
I've seen a couple of really nice takes on the theme though. Cold Ones as mounts with IG plastic soldiers as riders (tried to go that route, not easy. Cutting, greenstuffing and repositioning the legs to the mount is a bitch, at least for my limited skills). Another option I've seen is offroad bikes as mounts. Take a peek at coolminiornot, I remember seeing a couple of inspirational takes on the theme there.