Oftentimes, I don't know where I placed my Android around the house. Is there a way to make it vibrate and emit high volume sounds/music that will help me find it?
Four come to mind:
Each goes about it in different ways. Phoning Pigeon probably has the lightest touch. You pre-define one or more phone numbers with the app. Then, if the phone receives two consecutive calls from one of those numbers, it will turn the ringer on at maximum volume.
Where's My Droid is similar, but you send an SMS message with specific text.
The Lookout siren is very loud; you'd have no trouble finding it. The app has several other functions as well, including virus scanning and backing up your data.
Prey is similar to Lookout's tracking and probably wouldn't be as useful for finding a misplaced phone in your house; it's more for tracking a phone that has been taken. It might work for you, though, and there's no risk in checking it out.
If you've lost the phone before you remembered to install one of the mentioned apps, you have one more option: Plan B (from the same people who developed Lookout).
Basically you install it after the phone goes missing and trigger it via text message.
I use wheresmycellphone.com, rather than downloading an app. Works great!