Grey Knights are still the best army to do this with, I think. I have a list on the GK forums right now that I kind of like; You take a GK Librarian as your HQ, stock it with some Terminators as your elite 1st Chapter, and then take detachments of Legion of the Damned to act as Rubrics... Then you can throw in the Inquisition Mini'dex to have some non-astarte sorcerers and some Propsero Spireguard in the form of Acolytes, OR you can take covens of Psyker henchmen. Of course, the Legions of the Damned are post-Rubric, but I think they make better Thousand Sons than Thousand Sons do.
Another option now would be to throw in the Tempestus for better versions of Spireguard. OR for something truly radical, you could use Sisters. They're the most elite 'human' statlines in the game, have weaponry that suggest their nearly as good as the Sons themselves, AND they have 'Faith', which is (from a Sons perspective) like a cantrip or minor sorcery.
But honestly, I don't think I'd ever give up Grey Knights as the core unit. None of the other armies can do the job well enough with psychic powers. You really really should have Divination in the army, something I still feel the codex Thousand Sons need. Only Tiggy can do that, right? Although now that I think about it, I t hink one of the FW special chapters had Divination available. I can't remember.