Scorpions are great for footdar, speed, solid saves, good damage output, good speed and has a nice special rule for deployment, their pistol and grenadies come in handy and I like to army the exarch with biting blade. Incubi are another great option here.
Harlies troupes on foot are fantastic, just tool them up with a caress, a unit of 9 took down Magnus the other night in two rounds of melee combat. Susceptible to volume of fire, so make use of their speed to keep them out of rapid fire range. Upgrading the pistols is not needed, you want them to be punching things rather than shooting anyway.
Poor Banshee's, just too squishy and they need Jain Zar to avoid overwatch, only really useful against T3 armies.
Shadow Spectres, so far they have been more of a distraction unit, with the enemies sending lots of fire their way, but a squad of fast moving heavy flamers is going to be high on target priority.
Reaper are still the bomb and don't marine players know it lol, these guys are champs, and are an auto-include in my lists.
Rangers, basically just a screening unit for Illic, too many autohit things floating around, mostly useful against Guardsmen to pick off characters.
Swooping hawks, solid options against T3 armies, but you want them as a cleanup crew and shooting first, Horde of conscripts will just take the damage and send a lot of shots back at them.
Dire Avengers are a great unit, but they need to be the unit that finishes something off, their armour save will not stand up to high volume of fire at AP 0, let alone an inferno boltgun. Just really squishy given their point costs.
WraithLords, these guys just get shot, very quickly, no invul save, can't be screened, degrade, so if you don't get them into CC they just become average.
Avatar of Khaine, small enough to be screened, has an invul save, good armour save, tears stuff up, but lots and lots of points, the screen unit will get shot, a lot, so you need a lot of bodies around him.
I wouldn't mind trying out Avatar+Asurmen+2 full squads of DA's.