I was just there last month; stayed at New York, New York for only a hair more than the Stratosphere, but the location is a lot better for accessing most of the Strip. Since you're staying at the Stratosphere, I recommend going to the top; the view is spectacular. I didn't do the rides, but apparently the spinny one is pretty cool. Not my thing.
By far the most fun I had was just walking up and down the strip, going into all of the casinos, just checking out the architecture and the unique ways each casino finds to go to excess in basically every conceivable way. Bellagio is good for the indoor garden and you absolutely have to see the fountains. Stay for more than one show; they're frequent, and some of them are significantly better than others. Other than that, you'll find stuff to do basically everywhere. If you can swing tickets to Cirque du Soleil, virtually every casino has their own show going (I've heard good things about O and Zumanity). Treasure Island has a campy show every 90 minutes with pirates and fireworks. But I think the best enjoyment derives from wandering around and trying to take it all in; it's all just so massive and utterly ridiculous.
Oh, if you're interested in going off-strip, you can head North and go to Fremont Street, which is covered by a TV 4 blocks long. Kinda cool. Don't eat over there though; you will die.