iOS (Jailbroken): Notification Centre is great, but sometimes the banners can get in the way of what you're doing on your iPhone. MiniBanners is a jailbreak hack that provides you with smaller banners so they're less intrusive.
To install the hack, just search for it on Cydia, install it and restart Springboard when prompted. When you're done, all your notifications will be smaller. (See the above image for an example.) If you like banners the way they are but wish you could make them smaller or customise them in some way, check out SimpleBanners instead. Both are free to download from Cydia.