Dedicated Hosting / Dedicated Server
You exclusively lease an entire physical web server (not shared with anyone) where you host your web site and you have total control over it. CPU and RAM resources are only yours to use and you can host multiple domains or a single web site. This is one of the most expensive types of web hosting, used by large companies, data centres or Internet professionals.
You purchase a dedicated web server for your exclusive use, but you have no access to your system files, which are reserved to the hosting company, you have no control over your web site core files and data but you don't have to worry about server management.
You own resources – an entire physical server and bandwidth - that you can customize at your own need, so you can do whatever you please to do but you have no support from the hosting company. You are fully responsible for your web site and server. This is the most expensive form of web hosting available.
Most known providers of dedicated / managed hosting are:
Inmotion, DedicatedNow, SingleHop, UltraHosting, Acenet, Aplus, Lunarpages, 1and1, ServerPronto, XL Host, GoDaddy, SingleHop, ThePlanet...
Shared web hosting
You share server space and resources with other web sites. Each site has on its own partition, or section (place) on the server to keep it separate from other sites. Your web site is may suffer from slowdowns and you may also have inconvenient neighbors such as gambling web sites. This is one of the cheapest types of web hosting, generally the most economical option and also the most commonly used across the web as many people share the overall cost of server maintenance...
Virtual hosting service
This is similar to shared hosting - you get your web site hosted on a virtual machine that runs inside a shared server. Each virtual machine has its own independent operating system that can be rebooted without affecting other web sites, but it uses the shared resources of the web server (CPU, RAM, etc.) This is one of the newest types of web hosting and it fills the gap between dedicated and shared hosting. You have an independent hosting space that uses resources of a machine that is not exclusively yours to neither use nor manage.
Shared / virtual web hosting prices are lower than a dedicated web server because many customers can be hosted on a single server. This is the most fitting way of hosting for 99% of web sites.
Most known providers of shared / virtual hosting are:
HostPapa, BlueHost, Yahoo!, DreamHost, Telus, GoDaddy, PowWeb, CertifiedHosting, RackSpace...
Your web site is operating on multiple connected servers, you host it on a server cluster and you purchase only the resources and traffic your web site uses in a pay-as-you-go manner, instead of limited to a single server. This type of web hosting is one of the cheapest, but it also exposes you to security threats and your web site data is accessible to company administrators and other web site owners.
Most known providers of cloud hosting are:
Cloud.bg, RackSpace, NetDepot, ReliaCloud, VPS.net...