I suppose Mark G. will be the person to ask about these, since he'll be the one borrowing them, but here we go just so they see the light of day:
CHAOS SPACE MARINES: (Alpha Legion, 400pts)
Troops: 8x Chaos Space Marines
-Asp Champ with PF
-mounted in Rhino w/ Havoc Launcher
Elites: 5x Chosen
-3 flamers, 2 meltaguns
-mounted in Rhino w/ Havoc Launcher
The Chosen can infiltrate, or outflank if held in reserve. And the two missile-armed Rhinos might be a big plastic hassle for people to deal with at this level. But it's a small list, only 13 minis, and only 8 of them are scoring.
SPACE WOLVES: (13th Company, 400pts)
Troops: Grey Hunters x10
Elites: Wolf Scouts x10
-plasma pistols x2
Like the Chosen, the Wolf Scouts can infiltrate or outflank, or even come in from the enemy's own board edge using their special rules. They don't have quite the ranged punch of the Elites, and they don't come with their own transport, but then again there are 5 more of them.
These lists are a fair amount alike; both have a mobile Elite element that will probably get devoted to anti-vehicle work before turning on any remaining infantry. The CSMs have more punch, but might be more brittle, since they have only 13 men to the Space Wolves' 20. On the other hand, the CSM have an extra APC, and both of them are much shootier than the Space Wolves' vanilla ride. Both of these lists will have the (mild) added complexity of the Infiltrate/Outflank rules to deal with, but I don't think that will make them too much of a headache for a starter army.
I've also toyed with pulling two of the Wolf Scouts and their Rhino; if I did this, I could give them an 8-strong unit of Fenrisian Wolves for some additional melee punch, as well as an additional maneuver element. But at the moment, I'm not sure that losing the mobility of the Rhino for the only scoring unit is worth the addition. They'd certainly be the 'sideboard' unit for this list.
And storyline-wise there's no problem with them; having spent the past 10,000 years or so in the Eye of Terror, I'm sure any Emperor-fearing Sister of Battle would attack these guys first and ask questions later. Frankly, I'm starting to sell myself on these guys; if Mark doesn't want to play them I might (especially since all my Dark Angel stuff is on hold in case the current rumors about them getting a new codex sometime this summer wind up being true).
Oh, and the third possible list, in case Mark surprises me and wants to go swarmy:
TYRANIDS: (Hive Fleet Name-to-be-determined-later, 400pts)
Troops: Genestealers x10
Troops: Termagants x18
Troops: Hormagaunts x20
Elites: Zoanthrope x1
The Zoanthrope will act as a half-assed synapse creature to keep the gants and gaunts on a slightly shorter leash than their instincts would permit; it'll also be a potential anti-vehicle unit assuming the stealers don't crunch the vehicles up first. They'd be even more straightforward than the two lists above, and having 4 units instead of 2 will probably be at least a little useful (particularly when 4 of them can hold objectives). Also, I priced this list out from memory - I might be 10 points off on the price of the Zoanthrope, which means two more gants have to go bye-bye (or two gaunts, and suffer the indignity of running a 398-pt list instead of using all 400). One of the best things about this list is that it's already built, and Nids are supposed to be tailor-made for the dip method of painting.
As for the Traitor Guard, I think they'd be too wonky for someone who doesn't own the rulebooks to work with for a first-time list; I must admit, however, that they look better and better. My Eldar are, conversely, looking worse - I'm just not sure that the two Vypers in that list can reliably (or even semi-reliably) handle 2+ Penitent Engines. Of course, having said that, I do have the odd notion of replacing one block of Dire Avengers with some Fire Dragons, and using the Vypers to mow down infantry like Khaine intended....