I haven't seen a full adhesive screen protector in quite some time, but I do admit I won't pay more than $15 on one so maybe there's some to be found at a higher price point.
I personally use Supershieldz and an Otterbox case and it's absolutely fine and I haven't had any issues so far.
If you're concerned more about scratches than cracks there are some "wet" screen protectors which are basically soft plastic that you apply to your phone after spraying liberal amounts of liquid on your screen. Here's an example of that for the G8. A warning to you: they're much harder to apply correctly. You get maybe two attempts to get it right and then you either run out of spray or have to use the second screen. I failed installing them a few times in the past. You want a very clean environment because anything trapped under the screen will be very hard to clear out without having to restart. My cat's hair ruined one or two.
My combo:
That case can be found for 10 dollars less if you buy it without the Otterbox shipping packaging here