Without reading too many more posts, here's some of the ones on my list:
Scott Steiner. never considered him much for a single wrestler, but he broke from his brother Rick, and then reappeared as a steroid freak a few months later. He was a pretty well built guy before, but he almost doubled in size in less then 6 months.
1-2-3 Kid. was a complete surprise to see him grow into Xpac and the like.
HHH he had talent, and size, but was an odd character as Hunter Hearst Helmsley the rich fop, but DX made him a star.
Mark Henry never thought he'd even be around in 2001, let alone 2007. should have let his fat ass go years ago, but he's a company man willing to do anything (Sexual Chocolate? Remember him? and Mae Young?) to stick around were others have more pride.
Gregory Helms. in WCW was part of boyband wannabe's but came to WWF and took off first as fanf fav, and now as a heel.
Lashley thought he would be a temp replacement ot fill in for the departed Lesnar. but he's shown some real talent, and is growing better on the mic.
Chris Masters would have thought he'd have joined the likes of Stasiak and Ohare.
Cade and Murdoch never expected them to amount to more then a glorified jobber team with the occassional run of wins to get a title shot against weak tagteam division on raw. oh, wait. that's what they are.
London and Kendrick always thought they had amazing talent, but didnt' think Vince could be convinced to let a cruiserweight tagteam do more then a short stint at the top. thought they'd be stuck as single cruiserweights until Vince dropped them like he does all of those size.
DIVA SEARCH should have stayed a 1 year thing instead of become a recurring event.
The Miz should not be on tv, but at least he's finally in ring instead of talking all the time.
the Kind jerry lawler as an announcer. was good, but thought he was too much of a reverse of JR to fit together well. but with Monsoon leaving for health reasons, Vince to get more interactive, and Heenan in WCW, no one else to fill the role since Jesse Ventura had leaft wrestling for politics.
Batista came in as Deacon Batista, working with Brother Dvon during the short D-boys split. THought he'd go the way of other similar sized and talented guys, Bull Buchanan, Tyson Tomko, and Luther Reigns and be gone quickly. But was put with HHH and the rest in Evolution(poor remake of 4horseman)
Randy Orton really didn't think much of him at first and still don't really, but can't deny that he does what he's asked to do in the ring.
Cena, never saw him getting as big as this, but thought he'd do ok as a steady IC champ/contender
Rock. never thoguht he'd go anywhere even after he started tweaking and joined the Nation, which is where his character really exploded. All his catch phrases and moves started then, and that was back around 1996-97 during the attitude era and like austin, he's coasted on his reputation sincethen never really being forced to try and grow from that stale character.