The American Society for Biochemistry and Molecular Biology (ASBMB) has recently launched a website for summer undergraduate research programs. So far, 120 programs are listed, and more are added every day. Check it out!
The Undergraduate Research Center at UCLA has compiled a list of research opportunities for their students who are interested in summer research at institutions outside of UCLA. You can use this document too, click here for a copy. Deadlines range from late December to mid-March.