Have a Saturn? Car key won't go into the ignition? You're not alone! Before you take it into the shop and start spending hundreds on diagnostics and replacement parts (some of which may be completely fictitious and made up by the dealership!), here are a couple things to try first, and also a way to help prevent the problem. If your car is like mine, you won't need to do anything more complicated or expensive.
Basically, near as I figure it, the problem arises during hot summer days when heat expansion in the steering column causes the ignition to go slightly out of alignment. To fix it, all you need to do is bang on it from underneath. Just use the base of your palm and administer a couple good whacks upward. The key should slide in easily after that.
There's also an easy way to keep it aligned afterward. When you've reached your destination and turned off the car, pull the key out of the ignition and then immediately slide it back in again. It may take a bit of jiggling to get it in the second time, but it should still go in. After that, when you next return to your car, the key should go in fine.
If the car key will go into the ignition but won't turn, it may have locked. This is a "feature" of all cars, not just Saturns. To unlock, put your foot on the brake, then turn the steering wheel while gently pressing the key in the direction you want it to go. If it doesn't work one way, turn the steering wheel the other way.
The above is how I solved the problem in my own Saturn. If none of those work for you, and/or if you have an additional solution, please let me know in the comments.