First of all, you can find a complete listing of them at:
as well as many other sites (Google Ascii).
You can add these characters simply by holding down the ALT key and typing in a numeric code. For example, for the degree sign, hold down ALT and type in 0176 ... and ° appears.
Other codes I use are:
0167 § (I use this in my signature!)
0177 ± (Plus/Minus)
There are others but these suffice for most things that are not already available on the keyboard (basically, the keyboard is programmed to all Ascii codes).
Hope this helps your postings!