It depends what you mean by 100% uptime. If you want real 100% uptime, you won't find it at a shared host. If you just want a guarantee, it's not all that uncommon, but keep in mind that it is only a guarantee. If (and most likely it will) uptime drops below 100%, you get SLA credits.
Well you will not find allot of Datacenters that provide 10$ hosting accounts. Most datacenters costs millions work with hosting companies since they are not interested in 10$. Except Liquidweb and other companies that own small datacenter you are probably get a better deal with a company that works directly with a datacenter. As for 100% uptime that doesnt exist. Nothing in life is 100% bullet proof except death.
You will find very good hosts that can provide you 99% uptime but dont expect them to give you unlimited domains and unlimited traffic kind of deals.
Host-tracker told me my site (monetos.net) had 100% uptime at Downtownhost.com. I think you may want to check this company
That's good for you, but doesn't really prove anything about the host. They have a server that's doing fine and running good. But what about the moment it takes a dive for whatever reason? How long it takes for them to get it up? Are they going to sit on the problem, or swiftly correct the situation?
Unless there's a some sort of cluster/failover solution - essentially more than one server running your site - 100% uptime isn't possible in the long run. Done right, it ain't cheap.
Usually people asking for "100% uptime" just mean reliable server with good network speed and decent uptime.
It could also you got lucky to be in that server. A company has as many uptimes as server they have. Also some siteuptime trackers dont work very well. It could be that your site is up from Canada and the United states but not in Europe. If the monitoring is in the US it will just show online.