Most surprising? One really can't look beyond Alex here. To go through a field like she had in Warsaw when she had never even played a WTA main draw match previously, never beaten a top 100 player previously and never been ranked in the top 200. Prior to Warsaw it was clear Alex was improving but this sudden bolt really could not have been anticipated at all.
2nd place has to go to Kimiko. At the time of her win she was a day short of her 39th birthday. Her comeback to the tour had been going for about a year and a half. And she had yet to win her 1st WTA maindraw match during that 1 and a half year comeback prior to Seoul, although she had several times come heartbreakingly close. I recall being so happy when Kimiko won that 1st match against a lowly ranked WC. But then to see her outlast quality opponents like Kleybanova, Hantuchova, Kirilenko and Medina Garrigues was actually as shocking as it was uplifting, and it really couldn't have been more uplifting so we are talking very very high on the shock-o-graph. Players just don't win titles at 38 years old, at least that was the preconcieved wisdom before Kimiko broke the rules of what was and what was not possible.
Schiavone, MJMS, Rezai and Makarova probably all ranked around equal for me. All outstanding players in their own ways capable of outstanding things who simply had a week when everything fell together for them. But although all four had some wonderful wins during their runs none of them did anything during those runs that we didn't already know they weren't capable of doing already. Schiavone, MJMS, Rezai had all demostrated their abilities to beat top players on clay prior to their big moments and Makarova had done the same on grass.
Lisicki's win I would rank below the others in terms of surprise since the field she beat wasn't nearly as impressive as that of Schiavone, MJMS, Rezai and Makarova and unlike Dulgheru and Date-Krumm she had already established herself on the tour at the time of her win. Honestly I remember at the time hardly being surprised at all.
Clijster's win was definately very surprising but only because it came so quickly after her return to the game. Had Clijster's won the AO instead of the US Open I wouldn't have been the tiniest bit surprised. And Clijster's had won a Slam before, so for me this one is in the same ballpark as Lisicki's win.
So in order...
MJMS (I put her of 4th out of this group because the truth is I had a lot of belief she could do this prior to this win