Just two years ago, another possible species of human that co-existed and possibly interbred with modern human species was discovered in a cave in Siberia. As of now, nothing is conclusive as only a single finger bone has been analyzed. DNA analysis of this bone show it to be not modern human (Homo sapiens) and not Neanderthal (Homo neanderthalensis). It has been preliminarily named Denisova hominin or Woman X. No genus or species has been assigned as more data is needed.
http://en.wikipedia.org/wiki/Denisova_hominin
Another species of human that existed during the same time as modern humans is Homo floresiensis, also called "hobbit" as a full grown adult was only 1 meter tall. Homo floresiensis is still under review and is currently a subject of debate.
http://en.wikipedia.org/wiki/Homo_floresiensis
Interesting stuff. The Homo genus all together is an interesting subject.
http://en.wikipedia.org/wiki/Homo