A good developer will add this option to their app: disable accelerometer. We've seen it in some Twitter apps and even our own WPCentral app has a "lock portrait view" option. Still, there are times when you want to do this globally because perhaps you can't sleep and want to use your phone while lying on your side in bed--hey, it's your world!
In that case, Windows Phone Hacker has provided a neat homebrew tool that disables the accelerometer on a global but temporary basis--great for those odd moments when you just don't want the phone rotating your apps.
That's the good news. The bad news is this is only for interop-unlocked Samsung and LG devices, meaning if you're on HTC or Nokia, you're left in the cold. Plus, you'll have to reboot your phone in order to gain back the accelerometer functionality, suggesting this isn't as elegant as we'd like it (but that's not the fault of WPH, who did what they could).
For those of you interested, you can grab the app here at Windows Phone Hacker to side load. Remember, only Gen 1 Samsung and LG devices can use this app. Finally, check our all the other homebrew Windows Phone apps here: wpcentral.com/tags/homebrew Thanks, Carlos, for the tip!