Off the top of my head here, based on the work they are currently doing and how they are being used (as opposed to my actual favourites):
1. Y2J - An awesomely timed and played return. If the WWE plays their cards right, Jericho could become the no 1 drawcard they have been craving, since the departure of Stone Cold and the Rock. It is a little fanciful (but not totally impossible) but if worked right, with an undefeated run, Y2J could have a wrestlemania passing of the torch match with the Rock at Wrestlemania. I fully expect the WWE to botch Jerichos run up, but at the moment, he did well.
2. Umaga - Nothing special, just a pure old fashioned bad guy. It is a shame they took away Estrada from him and a shame that he is starting to lose his invincibility to lower and lower guys, now he cant even beat Jeff Hardy, who he used to dominate. Still, there is some great potential to increase his run. He needs another victory over HHH even if it is just a dominating PPV. I think there is so much they could still do with him, if they actually make him win and keep the invincibility he has. Undertaker, Batista and Great Khali would be three great wins for him, as would a win over DX (especially if it involved a 3 minute warning reunion) - Another unrealistic suggestion from me.
3. Mr Kennedy - Starting to lose a little too regularly, but the Kennedy catch phrase is still awesome which is amazing after so long. He needs to dominate someone in a feud. Maybe an intercontinental reign would help.
4. Fit Finlay - Absolutely amazing what WWE has done with Finlay, imo. They wrecked nearly every WCW superstars career that they touched, yet they made the dreadful wrestler finlay into a legitimate main event wrestler. In fact, i think that the Finlay Hornswoggle angle has been played perfectly. The attack on Khali and against Carlito was great.
5. Santino Morella - I agree with the growing consensus on this board. I dont know why, but Santino has officially grown on me. He is dreadful in the ring so far, his parts were predictable and he is jobbing to everyone, even Ron Simmons and Jerry Lawler. Yet he is flourishing. I actually think he has done enough to get a full scale run as a main event heal. He should pin and injury Jerry Lawler. He should outsmart and pin Stone Cold at a pay per view. he has the ability to be the cocky, funny heel that the WWE is lacking so badly.