Just because genjutsu doesn't work on him doesn't mean he's invincible :|
Let's see -> versus Itachi he'll have to deal with:
1) An impenetrable Susanoo (via Yata Mirror), so his attacks with wooden/metal puppets will be rendered useless. Iron sand should be interesting though.
2) Itachi can identify the source of Sasori's chakra. You know, with his
sharingan.
3) Sword of Totsuka. Or really any of Itachi's offensive weapons. Ten bucks says Itachi pierce's Sasori with a Kunai from a blind spot xd.
4) Amaterasu. Someone said this wouldn't work ... I'm not sure why not, but even if it's thrown out Sasori is still screwed.
Now then, versus Kisame:
1) Samehada, great for cutting chakra strings and slowly exhausting Sasori's chakra levels (Sasori is no tailed beast

)
2) The big bubble thing. Drown Sasori if that's possible. If he somehow can still breathe underwater, at least the water will render his poisons and iron sand pretty much useless. Puppets will move slower.
3) That massive shark bullet thing. Sasori's chakra is doomed.
Hmmm, I'll stop there.