Lois Lane (Erica Durance) was introduced in season four of Smallville when she comes to investigate the mruder of her cousin, Chloe Sullivan. However, when she finds out Chloe is still alive, she enrolls in Smallville High to finish the high school degree she never did.
As of season seven, Lois has been a reporter for The Daily Planet. Though her and Clark often butt heads and love to tease each other, there's definitely going to be a Lois and Clark in the future. Duh, have you read the comics?