For Microsoft Windows:
Note: Use all this codes with the combination of Alt. For Example you need to type © than press and hold the “Alt” key and type 0169.
© – 0169
® – 0174
â„¢ – 0153
• – 0149
§ – 0167
†– 0134
‡ – 0135
– – 0150
— – 0151
¶ – 0182
Â¥ – 0165
§ – 0167
¼ – 0188
½ – 0189
¾ – 0190
À – 0192
à – 0193
» – 175
÷ – 246
ø – 0248
þ – 0254
ß – 225
For Mac OS X:
These are a lot easier to figure out on your own. You basically just use the option key as a modifier with any other key and see what happens. Here is a chart of the most popular ones:
© – Option+G
® – Option+R
â„¢ – Option+2
¶ – Option+7
• – Option+8
§ – Option+6
– – Option, then minus sign i.e. Option+-
— – Shift+Option+-
†– Option+T
For a more complete list of the character palette for the Mac check out this page, for accents, check out this page.