If you want something fun and new, I can't recommend anything better than using Cypher in creative ways. He's a 190 point model you can add in that joins your primary detachment.
I wrote an article that lists all his benefits, though bear in mind my original message in it with using infiltrate is in murky waters due to a rules debate.
That said, there is no debate on whether or not Cypher gives you Outflank, so if you more or less ignore the bits on infiltrate, you may find it useful.
As you may see in that article, I take an Inquisitor. They are pretty good assets to an Astra Militarum army as they make your Guardsmen less weak and when you give them a few toys they can do some wacky and interesting stuff, while solving morale issues.
Taking 5 man squads with the Militarum Tempestus is decent if you just take the Command squad and 1 5 man squad. That way its just opportunity kills.
Imperial Knights are very good gameplay wise, but not overpowered, they're generally accepted and they're great models. Though the price of the model is discouraging, its probably cheaper than buying an allied detachment. They may appeal to you because they're very aggressive and different to using Russes.
Space Marines are iffy. Tactical Squads are basically a joke, Scout Squads give you nothing and unless you're taking Bikes in Troops you're wasting your time and your points. The only appeal of a Drop Pod ally is getting Sternguard really, and that becomes a bit silly of a prospect when you can put out the same amount of firepower from across the board already, without losing the absurdly costed unit in a turn.
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2,000 points 
265 point detachment
Iron Hands: 1,850 