Think the back four and midfield are a near certainty, just a question of who plays upfront. One of Kuyt or Crouch.
Mascherano won't start, I'm fairly sure of that. I think he is a fantastic player, but Xabi and Sissoko have proved to be such a good partnership in big European games that it would be almost a crime not to start them together, with Stevie (although I don't think it's his best positions, prefer him on the right) will play behind the striker; giving Makelele a job to do, and although I rate Makelele, I can't see him managing to keep tabs on Stevie for the whole game, with his energy and movement.
Pennant will likely start wide to stretch things and given his recent form, I think deservedly. I think this may play a part in the decision of who to play upfront, and it may mean that Rafa will go with Crouch. No point try to second guess the man however, he could well suprise us all - and probably will.
No doubt Riise will start on the other flank. Mark needs time to settle in and probably isn't ready for a game like this, and although Riise's form has been questionable, his experience at this level, and his performances against Chelsea in the past, signal that he is an almost certainty to start on the left hand side, with Gerrard tucked between the two wingers in a 4-5-1. A sturdy back four of Finnan, Carragher, Agger and Arbeloa is probably the only sure thing for this game, other than Pepe in goal.
Although I think a 4-5-1 is fairly predictable, or to be more precise a 4-2-3-1, I think Rafa's tactics/game plan are almost impossible to read. While he send this fairly defensive (I'd say solid, stable or organised, rather than defensive), that doesn't mean we will sit back. The energy we have in the side means that we might take the game to Chelsea in the first 15, catching them off guard and scoring an early goal with a tight side to keep a clean sheet (or only conceding 1) after that, which that side in particular, is more than capable of doing against a tired Chelsea side.
It's going to be interesting. The only thing we can be certain of is that Rafa will suprise us.