hey oldman,
There is a little more variability in what residencies look for than the med school apps. In general, however, the things that make a difference are:
USMLE Step 1 (some programs weigh Step 2 heavily as well, but not most)
Clinical Grades: This generally means third year and early fourth year grades, espcially the one in your specialty of chioce and the biggies Medicine and Surgery.
Dean's Letter: This is only important in that it usually gives personal evaluations of your clinical performance and gives a general ranking in you school.
Research: If you want to go to a university program, this will help. There are many great private hospital residecies that couldn't care less.
Interview: This can really make a difference. This is more like a job interview than med school. The interviewers want someone they and the rest of the staff and residents will enjoy working closely with for 3-7 years.
Personal Connections: MUCH more important than in med school. This is why some people in competitive specialties do rotations at places they want to go.
Pre-clinical (first 2 years) grades: As long as you do OK, not looked at much.
Extracurriculars like AMSA, AMA, outside interests etc play relatively little role except in letting them know that you have a life outside of the classroom.
The emphasis can greatly vary by specialty. Ortho people almost always do audition rotations at programs. Peds and psych seem to pay more attention to personality. Rads may look a little more at preclinical grades like anatomy. Etc, etc, etc.