We have a spinner and it's great exercise, we have a couple DVD's that work your butt off. However, it's a PITA, any day outside is better then riding in the basement. I would make sure I had all the gear I needed to ride all year first and then get a mag-trainer or rollers. Spinners are nice, but outside is best. The bad part it's expensive to buy a couple different weight jackets, gloves, jerseys, tights, shoe covers, warmers, etc... I usually can nail the layers needed for cold weather cycling, but have a lot of stuff to be able to pick and choose what I need for that day, etc...
John