Probably the most useful special character on this forum is the degree symbol ° - but there are plenty of others:
To type the degree symbol °, make sure that your keyboard Num Lock is enabled. Press and hold down the Alt Key, then type the numbers 0176 using the number pad on the right hand side of your keyboard. Then release the Alt Key and the degree sign ° will appear (NOTE: these features also work in Microsoft Office).
To type µ (the Greek letter mu), hold down the ALT Key while you press the numbers 0181 and then release the Alt key.
To type ±, hold down the ALT Key while you type the numbers 0177 and then release the Alt key.
To type ÷, hold down the ALT Key while you type the numbers 0247 and then release the Alt key.
To type ×, hold down the ALT Key while you type the numbers 0215 and then release the Alt key.
To type ∞, hold down the ALT Key while you type the numbers 236 and then release the Alt key.
To type ≥, hold down the ALT Key while you type the numbers 242 and then release the Alt key.
To type ≤, hold down the ALT Key while you type the numbers 243 and then release the Alt key.
To type ½, hold down the ALT Key while you type the numbers 171 and then release the Alt key.
You can also use the sup and sub buttons to make superscripts (x2) and subscripts (H2O).
