Fellowships are available for graduate students in EECS who are exceptionally well qualified. Unlike assistantships, fellowships usually do not require the student to perform any duties. Fellowships are extremely competitive and generally applicants will need to have a cumulative score on the GRE greater than 2200 to be considered for this type of financial aid.
The monetary award varies depending on the fellowship but is generally similar to that of a research assistantship. The Fellowships are awarded only for the first academic year of graduate study--after this the students are supported by regular assistantships.
Follow this link to read about other financial aid opportunities, such as Research Assistantships and Teaching Assistantships.
The Northwestern University Office of Fellowships is a valuable resource that offers assistance in your search for national and international fellowship competitions.