It's unlikely a virus could wipe us out, because the more lethal the virus, the more likely it will burn out by killing too many people too fast and running out of hosts. A really bad, easy-to-transmit, very lethal virus is more likely to result in a population bottleneck than an extinction. Plus, almost certainly some humans will find themselves immune.
One exception could be an immunodeficiency virus, especially one with a long latency period. Something like an airborne HIV could probably kill the entire species. But even then, there might be hope that small pockets of people - say on Sentinel Island or deep in the Amazon - might avoid infection and be the seeds of a new spread of the species once everyone - and the virus - is gone.
To really kill the species, you need 100% lethality delivered in a method that will still reach even the most remote human outposts.