What are they and what announced games do you think will gain cult followings?

Currently I can think of two:

Zack&Wiki

No More Heroes

Both of these games generated masses of internet hype, reviewed as very good (not superb admittedly) and sold poorly. For No More Heroes it was expected due to the fact that its the same for all Suda51 games but Z&W caught me by surprise.

What other games do you think will become cult games? 

gta 4?

I would add Little Big Planet to that list once it's released.

No More Heros hasn't really sold poorly. It debuted in the top 20 this week, which was far more than a lot of people expected. The budget of it cannot be too much..

Rayman Raving Rabbids would be a good example. The first one, anyway..

 You just named the single least cultlike game I can think of.

 LBP stands a good chance of gaining a cult following. RRR isn't really a cult game is it?

I think the PSN/XBLA offerings should largely be considered cult games, at least the more popular ones.

Some examples:

Everyday Shooter
Geometry Wars
Super Stardust HD
etc.

I think the new Ps3 game from Team ICO will probably have a cult following.

Folklore?

The next Team ICO game, most likely.

well for me cult games are:
geometry wars, mario galaxy, super smash bros brawl, zack & wiki, bioshock, LBP, no more heroes, phantom hurglass and locoroco
i would say that: nights, paper mario, gears of war, skate, elebits, devy adventure, dead rising, hotel dusk, potapon and whole pheonix wright should be here too but they aren't so damn perfect(but still those are really great games) to be consider as such a cult titles.