Listing all co-location providers in one thread would be quite a job, and quite a large thread
There are a lot of threads in the co-location discussion where people asks for co-location in specific areas, you might be able to find what you need by searching for old threads or specifying in this area where you need co-location.
Sune Christesen ActiveWebs A/S - Dedicated servers, virtual servers, server hosting and private racks in Denmark. Data Center Map - Worldwide colocation, cloud and carrier index with interactive map.
European-DDoS-Protection.com - Protection against DDoS attacks in Europe.
please list all the Colocation providers in this thread which will not only help me but will also help others finding the right decent and reliable colocation provider.
As mentioned, colo is pretty much regional. The "best" DCs will probably be pretty much limited to your closest large metro areas.
That said, there are major national and global players in the market like Equinix, Switch & Data, Verio, Digital Realty Trust that may have more of a national reputation for service quality. A lot of people consider Equinix a very good premium colo provider for example - with pricing to reflect that.
Still even the largest metro markets - SF Bay, Los Angeles, NYC, Dallas, Chicago - are probably dominated by local/regional players vs. just national players in the colo market. SF Bay has Hurricane Electric and 365 Main, for example, as pretty major local colo providers, though 365 Main is growing its presence nationally.
Colocation is not only regional, you also have to think about what you need such as.
How much space you need
Who you want bandwidth from
How much bandwidth do you want
Do you want cross connects to any one
How much density do you want to want
What kind of reliability
What kind of support
24x7 on site
how much you want to pay
There are so many options when it comes to colocation that you have to answer some questions first. There are many more questions than what I just listed. The biggest factor is how well you work with your colocation provider.