Your question intrigued me given that I loved Meyer's book The Host. Therefore, I decided to do a little research in order to find out for both us and any others fans of the novel.
Here is what I found. Meyer did, may still but not completely sure, plan on making The Host part of a trilogy. When attending a Question and Answer function on her novel, Meyer admitted that she had already (as of November 2009) begun to outline two more novels to follow The Host.
The names given in the Q&A were The Soul (the second novel) and The Seeker (the last and final novel of the proposed trilogy). Meyer, when answering about the possibility of follow-up novels, was not quite sure if she would go forth with the second and third novel based upon the fact that the the setting of The Host is a "dangerous place" and she is not quite sure about continuing the novel's storyline.