1) Something to do with Dark Matter- there are all these off hand comments about it in Mass Effect 2, so I wouldn't be suprised if it pops up as a kind of superweapon.
2) A plan that almost entirely relies on Shepherd and his squad fighting in a cover based system against enemies that, despite being different in every facet of their being, fight exactly like he does.
3) Nukes. If Russia's got 20,000 now, just think of the future possibilities...
4) Resurrecting Isaac Newton to come up with an ingenious plan. He is, after all, the DEADLIEST SON OF A ***** IN SPACE.
5) A plan that involves the Shroud of Turin, several pieces of the One True Cross, and a heck of a lot of Blessed Hosts.
6) Getting the Geth to hack into the Reapers with some Quarian help. This is kinda boring though, so...
7) The Second Coming. Let the Son of the Father judge the crap out of those diabolical machines!
8) An epic space battle over the skies of Britain that FINALLY lets us pilot the Normandy ourselves.
9) Resurrect Merlin and King Arthur. It could be like a Dragon Age crossover- pure awesomeness.
10) Lure the reapers into Wales, to be destroyed by my nations overwhelming hordes of chavs and single mothers. Oh Land of my Fathers...
Oh, and each plan has to involve Shepherd being allowed to go out with Tali again (with a minimum of 9 paragon hug moments), Shepherd being allowed to punch someone or do something badass that isn't automatically labelled renegade, Garrus kicking some ass in whatever manner he sees fit and Legion being made Space Pope. Which would be awesome.
Oh yeah, and something to do with the Rachni.