rumours started regarding the GF104, we heard about the GTS 455 and wrote about it here
. Back then, rumourville was talking about GTX 460 and GTS 455 as cards that were going to be first cards made with GF 104 GPU, and it appears that GTS 455 was on the roadmap but just not yet as Nvidia should launch two GTX 460 version on July 12th.
Well today, rumourville is still talking about the GTS 455 as a possible GF104 card and considering Nvidia's naming scheme, this one might end up to be much more crippled GF104 than the one on GTX 460 cards.
The specs are still blurry and nothing is yet confirmed so its still not clear on how crippled will the GTS 455 actually be. The launch date is also not confirmed at press time, as it is unclear if Nvidia is going to launch this one before GF106 based cards or alongside them.
The GTS 455 for now sounds like a "fourth card" that will be launched with GF104 as you have two versions of GTX 460 cards, a possible GTX 475 with full GF104 chip and the rumoured GTS 455.