Ever need to make a line break within an Excel cell? Sure, when you are typing a long description (like invoices). The secret to doing it is alt-enter. Yep, simple as that:
Quickie Excel tip: When you’re typing text into a cell, by default hitting Enter takes you to the next cell. However, to wrap your text in the current cell as you type? Hit up Alt-Enter.
Check out some more Excel keyboard shortcuts.
Source: Excel Tip: Wrap text as you type with Alt-Enter – Lifehacker
Lifehacker is building a great list of shortcuts for Excel. One of my favs is still the ctrl arrow key. It jumps to the next filled cell. If you combine that with shift, you get an ultra-powerful way to select a ton of data with one click.