In no order, the top 4 matches are without doubt:
Daniel Bryan vs Sheamus
2 guys that have had a breakout year. Sheamus is a 2 time WWE champ, but he wasn't ready for it at the time IMO. Now, he's more than ready. Daniel Bryan has proven to be an excellent heel champion. Really looking forward to what should be an excellent match.
CM Punk vs Chris Jericho
What more is there to say. The buildup is getting heated and personal, and there's no doubt that the match will deliver. 2 of the best in the business right now going head to head, it'll be a potential show stealer as far as in-ring performance goes.
Undertaker vs HHH
It's 2 legends inside HIAC at Wrestlemania. And if that wasn't enough, Shawn Michaels is the special guest referee. The match will be brutal, and who knows what the outcome will be (I suspect that WWE has something up their sleeve).
The Rock vs John Cena
The match won't be anything out of this world, but the occasion will be enough. I think WWE have done well with the little time The Rock has been able to commit to them. Plus there's the personal touch added which will make it a huge spectacle.
I am looking forward to the Orton Kane match, if they make it a no DQ match or something. Orton and Kane usually do well when they're given free reign to do stuff like that. But it's just another filler match on the card to me. I'd like to see that feud continue beyond Wrestlemania though.