UPNetwork -> Manga -> Dagenki Pikachu Dengeki Pikachu
This is the most well known manga series, the one by Toshiro Ono which is based on the anime. Most of the main characters from the anime are present here. There are many similarities to the anime, but also many differences. This series is complete.

Volume 1 - The Electric Tale of Pikachu
Volume 2 - Pikachu Shocks Back
Volume 3 - Electric Pikachu Boogaloo
Volume 4 - Surf's Up, Pikachu