Where have you read stories about iPad killers? There is nothing that is even attempting to compete with the iPad yet, and the only place I have even heard the term iPad killer is on Apple themed forums by people being snarky and sarcastic referring to $150 dollar Android tablets that have yet to be released.
Also, you must define what would constitute an iPad killer. Apple fanboys would never accept anything as an iPad killer because they will always have the App Store to point to as the great advantage. For me, personally, the first tablet that comes out that has HDMI out with 1080P playback, USB ports, ability to stream network shares and ability to customize the interface with a respectable battery life will be an iPad killer. A majority of the people on this board I suspect would never agree that something could be an iPad killer except another iPad, because there will always be SOMETHING about a competing tablet than can be mocked. Even if its an amazing tablet that is feature rich, it will still be criticized for the battery life or aesthetics or weight or some other reason.
As of yet, there is no competition even for the iPad. There are SEVERAL tablets that have been demoed that look like they will destroy the iPad, for me at least. The eeePad is shaping up to be amazing. A 16x9 screen immediately makes it better than the iPad, since watching HD content on the iPad leaves you with black bars. It also is coming with Android or Windows Compact 7, which looks absolutely stunning but is an unknown entity at this point. Next is the exoPC which is running Windows 7 with a very attractive GUI overlay. The big advantage of the exoPC is that it can run any windows software while remaining pretty and functional. The downsides are obviously that the OS is not designed around touch so there will always be quirks.