There are countless beneficial resistance exercises and it depends greatly on what you would like to accomplish, be it for general strength or for more specific objectives.
For my clients just starting out on resistance training I have them use traditional free weights – barbells, dumbbells and cable machines. I have a specific set of easy to learn exercises that I want them to master; they make for a great transition to more advanced exercises.
Cable Lat Pull Down
Overhead Dumbbell Press
Cable Seated Row
Barbell or Dumbbell Bench Press
Squat (either body weight, dumbbell or barbell)
Lying Hamstring Curls
Supine Pull Up (AKA Inverted Row)
Step Ups (up to chair height)
Standard Abdominal Crunches
45 Degree Back Extension
This list is not all inclusive and I make additions, eliminations and variations depending on the abilities and limitations of my client.