Well I think Kaldour would be the coolest, remember the chap who was an imperial noble folowed Tzeentch, leads an army of imperial knights, brettonian knights, arabrian mounted nobles, estelian, tilean, all decked out in the warped gleaming armour of their homeland. A mercenary army so awesome You'd have to change your pants every time you see them charge.
Lizardmen are hard, karnac's lizardmen need to be totally re-written as they're from 2nd edition, everything has changed, they can't have bows or swords and in the new lore the replacement of lizaerdmen warriors (saurus warriors) are completely sub-servient to the slann. In the old version lizardmen were the original occupants of the world before the slann and were driven underground by the slann, in the new they were created by the old ones as slightly dim slave warriors almost completely dependant on the slann. You could re-write their background to fit the new editions, but it'd be tricky and very unofficial, I'd be happy to help.
If you're set on doing a unit of renwon that's awesome and hasn't been done yet I'd suggest Beorg bearstruck and the bearmen of urslo, king of the Baersonlings, I think you'd do a good job on him and his warriors, plus he needs to be done for the Norsca mod, you'd be helping out a fellow modder with a faction that we'll have in the future. In this vein is another Norscan of awesomeness: Wulfrick the wanderer, you just have to make one model for him like Valkia.