Try doing different workouts on the elliptical to switch it up. Usually machines have programs that change the resistance and height throughout the workout. This will help keep the workouts fresh. Also, you can alternate during the workout whether you are moving your legs forwards or backwards. Again, this helps keep your body from being accustomed to the workout. Different speeds also help. Make altercations for each workout and that will help keep things fresh and allow you to continue to burn.
In terms of the bike, don't worry about your arms. You say you lift weights and that will be doing a good portion of toning for you! The cardio machines are going to help you burn overall fat while the weights help you burn efficiently and continue to burn after your workout as well as toning your body. Both are essential. Like I said before with the elliptical, to keep a bike routine fresh, continuously change up resistance and speed during your workout to maximize the burn.
Good luck!!!! You can do it!!!