Cogent is a bandwidth provider that offers A LOT of bandwidth at extremely affordable prices as compared to other providers such as UUNet, Level3, etc. Some people do not like Cogent as they claim they are oversubscribed bandwidth, meaning, offering more bandwidth than their network can handle. I actually find Cogent very fast and reliable so far.
Along with the cheap prices to the NOC, they pass on that savings to you, somethings less than $1/gig. Since Cogent is still a very new company, few years old, some people prefer the reliability and redundancy of having multiple bandwidth providers. You will notice that some fly by night server companies only have Cogent, in which case, you should stay away. You can find out more info about Cogent at: