We've done this before and you're best off served by searching past threads. Here are 2 arguments that haven't really been posted before:
1) Canon's and Sony's dust buster features don't appear to work in that they don't appear to be able to clean themselves. However the coating on each sensor does appear to make the dust less clingy than otherwise - and that means it appears to be easier to remove with a rocket blower. So they're both still useful, but not as good as Olympus' version.
2) All the manufacturers appear to be ramping up for new releases in Aug/Sept. While noone is expected to release an entry level DSLR (while each of these cameras has differing spec lists, they are each manufacturer's entry level model), waiting until each company shows where they're going in terms of new bodies and lenses might be a worthwhile exercise, and prices might come down too

Sony in particular has a lot to proove, although signs are it will meet expectations.
Were you to have to buy tomorrow, I'd reccomend the Sony, it has a lot of features the Canon and Nikon entry level models don't.