Animal Crossing Wii(assuming it does come out in NA this year). The DS version sold QUITE well. I'd say it's the only OTHER game announced for 2008 that is to be a pretty much guaranteed hit.

Some other games have the potential, if the Wii user-base bites. Boom Blox being a likely candidate(look at sales of things like Peggle to see what COULD happen).

Wow this guy was asking for mega hits and you folks jump on with just about every first and third party title coming out. Did someone seriously put Sadness, Sky Crawlers, Deadly Creatures, Tales of Symphonia, Fatal Frame and Fragile in the mega hit category? Sadness isn't even a real game so how can it sell a single copy let alone "mega" copies? In my opinion here's what we can expect to sell large in 08 on Wii thus far

Wii Fit(Guaranteed)
Wii Music(Damn near guaranteed)
Animal Crossing Wii(Very good chance of a few million sales)
Deca Sports(It can very easily ride the coattails of the Wii Sports popularity)
We Ski(If the balance board takes off, expect this game to sell very healthy)
Pro Evolution Soccer 08(At least in Others regions it will have good sales, should jump past 1 million, maybe 2)
Boom Blox(This is hit or miss, but it has mainstream appeal)

As long as they make Ninja Bread Man 2 I am ok.

I think with the currently lackluster launch schedule, there's bound to a slew of announcements this year!
KH 3, next Metroid, Starfox and perhaps a new Zelda may be among them as well as Wii Play and Wii Sports 2!
I also have the feeling we'll be show a new Mario RPG this year, possibly at E3.

 I think most people like me thought they meant good quality games.

That was meant as a joke, right?

GTA4 is not coming to Wii.

The best GTA the wii will get is San Andreas ported over from the PS2 :P

Go Diego Go and Sponge Bob Saves Bikini Bottom.

 Nintendo power already had a small article about GTA not coming to the Wii

It is confirmed that GTA is NOT coming to the wii. 

The game that Regie will announce at E3 will be huge.