I could swear I saw those IG on /tg/ the other day.
Anyway, I've got an 11k Chaos Marine army which consists of several smaller warbands, each with it's own fluff and squad markings/paint scheme.
I recently acquired 3k of Space Marines which are currently and slowly being painted up to a showcase standard for my local gaming club. They're also to be used as part of a doubles army with my friend since we're both playing Crimson Fists.
...Ed'c Desa Drec Tnays Lusac Du Yh Aht
Ubah Byhtuny'c Puq Yht Dyga Y Cdab Ehceta
I have a nice "little" Tyranid force which I've been using for a long time, and which keeps growing.
Just a tip for the "mass horde" style armies (IG, 'Nid, Orks): Paint a full squad at once. Prime them all, then do the base coat on each, then go back and work on the highlights. It not only goes faster, but since they aren't special characters having them all look virtually alike isn't a bad thing. Differentiate your squads (and special characters) rather than the individuals in the squads.