Below are the three type of resources with which you can begin your exploration of research opportunities and funding.

Harvard offices providing multi-disciplinary research support and advice
These are offices with staff and/or websites dedicated to providing guidance to undergraduates interested in exploring research opportunities at Harvard as well as outside Harvard:

Office of Undergraduate Research and Fellowships - Advises undergraduates interested in any kind of research in all fields.
Undergraduate Education in the Life Sciences - Advises undergraduates interested in life sciences research.
SEAS Student Affairs Office - Advises undergraduates interested in Science and Engineering research.

Databases of Harvard-affiliated research opportunities and funding sources
These searchable databases list both research opportunities as well as sources of funding to support undergraduate research. Note: these databases are not exhaustive. Research opportunities and sources of funding are constantly updating, and therefore many opportunities/funding sources may not be listed in these databases.

Funding Sources Database - This database lists sources of funding that support various endeavours in various fields. Use the filters to locate research-specific funding options in your field of interest.
Student Employment Office - Searchable listing of jobs, including internships, part-time jobs, and research assistantships with faculty and other researchers at Harvard.

Concentration resources
Concentration advisers, websites, list-servs - Each concentration at Harvard has dedicated advisers for guiding undergraduates through that field of study. Since the advising structure of each department varies, these advisers may have various titles including Director of Undergraduate Studies (DUS), Assistant Director of Undergraduate Studies (ADUS), concentration adviser, etc. These advisers are an excellent resource to get guidance on the kinds or research opportunities available in the field. Note: some concentrations have created web pages with information concerning research in their fields. These web pages are a good place to get preliminary information; however, you should always complement this by speaking with concentration advisers, faculty, TFs and other mentors. 

Student Groups
Getting involved with student groups and publications can expose you to research and other researchers. The following are examples of such groups and publications.