Lisa Lasalle was introduced in Superman: Earth One Vol.2. created by J. Michael Straczynski (writer) & Shane Davis (artist). Lisa is a outgoing, musical loving and very trusting woman who lives next door to Clark Kent in Metropolis.
She is very friendly to Clark early on with a clear attraction to him. Lisa openly flirts with Clark throughout the story and never really takes things seriously.
Clark's liking of Lisa goes as far as him letting her in to his life, telling her details about his past which up until he met her, he had not told anyone outside of the Kent's (save for the fact that he is Superman). He shares with her the story of his only real friend while growing up [Fuzzball, a cat he had saved from a pack of wolves].
Later on, despite not mentioning what she normally does to make a living, Lisa reveal that at extreme times of need she "hooks on the side", this does appear to upset Clark to a degree, however despite this, they remain close friends.
It's also worth to note that Lisa has seen Clark without his glasses on and is fully aware of Superman, yet she was still un-able to put the two together. This however changes in Superman: Earth One Vol.3 where finally, Lisa discovers Clark and Superman are one and the same. This does not change her attitude towards him and only strengthens their bond.