1. A recommended keyword suggestion system in communication with a computer network for suggesting a keyword and performing a search in a plurality of computer servers in the computer network, the system comprising: a computer processor and a database storage device for storing data used or generated in the processor; a search result providing unit, in the processor, configured for displaying a first set of search results associated with a certain keyword input by a user at a website, each of the search results listing a site on the network directly accessible on the network by the user when the each of the search results is selected by the user; a keyword extracting unit, in the processor, configured to extract at least one keyword associated with the certain keyword from a related search word database in the database storage device; a display score providing unit, in the processor, configured to provide at least one display score for the at least one extracted keyword, each of the at least one display score being associated with an expected revenue from advertisement of each of the at least one extracted keyword on a website; and a recommended keyword determining unit, in the processor, configured to determine at least one recommended keyword from among the at least one extracted keyword to be displayed on a website in addition to the first set of search results, based on the provided at least one display score; wherein the at least one recommended keyword enables the search result providing unit to display a second set of search results related to one of the at least one recommended keyword when the one of the recommended keyword is selected by the user, wherein the display score providing unit comprises: a Pay Per Click (PPC) value providing unit configured to provide a PPC value of each of the at least one extracted keyword; a Click Through Ratio (CTR) providing unit configured to provide a CTR of an advertisement region of a website where advertisements corresponding to the at least one extracted keyword are displayed; and a display score calculating unit configured to calculate the at least one display score of each of the at least one extracted keyword, based on the PPC value and the CTR, wherein the display score calculating unit calculates the at least one display score further based on a display frequency of the at least one extracted keyword for denoting a weight according to the display frequency, and the weight based on a number of times that the at least one recommended keyword has been actually selected by the user is assigned to the at least one display score.