Subway, Seoul

The prices are very low, mainly if you come from Japan. :) For only 0.5USD you can travel even 40 stations on the subway. Although I do not know, how does it work if you have to change line, I do not think it is a big deal even if you have to but an other ticket for an other 50 cents.

For getting around in Seoul the subway (metro or underground) is the quickest and most convient way. It offers a huge network with and good connections. A ticket costs you 600 Won only. But store it good, you will need when you exit the subway because there are barriers at the exits and they only open when you put in your ticket .....

The Subway is the best way to get around in the City. Its fast, cheap and clean. Most tickets for one way cost around 600KRW.
Signs are in English everywhere and a voice always anounces the next station. Eat/drinking is not forbidden but Koreans (like Japanese) simply don't eat there.

The subway system is the most efficient way of getting around Seoul. Station names, ticket windows and transfer signs are all clearly displayed in English as well as Korean.

Map (incomplete) taken from http://www.metropla.net/as/seou/seoul.htm

SUBWAY SUBWAY SUBWAY, although taxis are relatively cheap. Busses can be confusing, even for people that live here. Ask someone who knows, and see if they will go with you! Remember, traffic is ALWAYS bad, so taxi fares for even short rides can get expensive.

Subway: Very confusing until you get the hang of it. For some reason it was a lot harder to figure out where to go compared to subways in other places I've been to: (Singapore, Honkong, Paris, London, Tokyo, etc) Or maybe I'm just slow...
Keep at it and you'll catch on
Fares: Single Tickets to places within Seoul is 600 won (zone 1) or 700 won (zone 2), a transfer ticket is 990 won for zone 1 and 1090 won for zone 2.

Subway is the most important means of transportation in Seoul. The subway in Seoul was inaugurated on August 15, 1974, for the 7.8km section between Seoul Station and Cheongnyangni Station.

Currently, the Seoul subway system is made up of Lines 1, 2, 3, 4, 5, 6, 7, and 8. Eight subway lines and a surface line of the government-run Korean National Railroad (KNR) merging with them serve Seoulites and visitors most effectively. Colored differently between lines, Seoul subway lines link the farthest parts of Seoul and its satellite cities and cross each other at various transferable stations, marked by the symbol.

In general, subway trains operate at intervals of 2.5 to 3 minutes during the morning and evening rush hours, and at intervals of 4 to 6 minutes during the non-rush hours.

It is always crowded with many people and many cars. So, subway is the best way not to waste time on the road.
However if you are planning to ride on the subway, it will be better to avoid rush hours. It is really crowded and you wouldn't feel good about being jammed in the train -_-;.