Android's notification system is awesome, but I sometimes wish I didn't have to look so closely at the menu bar to see the details of an incoming notification. NotifierPro adds large, customisable, detailed banner menus to Android so you can see exactly who is emailing you (and what it's about).
The banners aren't unlike the new notification system on the iPhone, only a tad less intrusive (and better looking). You can turn them on or off for whichever applications you want, tell it to re-send the notification after a few minutes (so you don't forget about it), and even download new themes.
When a notification comes in, you can tap it to launch the associated app, swipe to the right to dismiss it, or swipe to the left to turn off notifications from that app or contact. You can show the notifications at the top of the screen or the bottom, and tweak lots of other settings. It does have a few quirks -- for example, it wakes up your screen with every notification -- but you can turn most of these off, so be sure to go through the settings before you judge it. It really does make Android's notifications better.
NotifierPro is a $2.51 download for Android devices. Most of the good features (such as notification details and contact pictures) are only available in the pro version, but you can test the app out before you buy with their lite version.