Once you link your different email accounts, a tiny popup message shows you how many emails you have on your inbox. To access them you just have to tap the number.
It has an interesting feature that plays a sound when you get a new email, so you know about it even if you're not looking at your screen or are using a fullscreen app.
Cobra Check Mail is very useful for users whose work depends on quickly responding to emails.
The trial version only lets you link one email account, and it expires after 30 days.