android special characters keyboard Under Winodws, if I want to enter extended characters (such as "«") I canuse the Character Map application and the Alt+keypad numbers (such as Alt+0171 for the "«").  

How can I do this under Android?  I know there are ways to do this under Linux, but is this infrastructure there under Android? 

Especially with tablets and phones and their special Android keyboards - which typically don't have Ctrl or Alt keys.
You might want to take a look at Hacker's Keyboard:

A full 5-row keyboard including arrow and Esc/Ctrl keys, intended for tablets.
Are you missing the key layout you're used to from your computer? This keyboard has separate number keys, punctuation in the usual places, and arrow keys. It is based on the AOSP Gingerbread soft keyboard, so it supports multitouch for the modifier keys.

 
It supports a bunch of keyboard layouts -- though I'm not sure about the &quot;special characters&quot; being inserted using alt sequences.
If you're mainly interested in being able to insert special characters (and don't care whether they are bound to alt-sequences or selectable by other means), I'd suggest to search the playstore for &quot;charmap&quot;. This will yield about 10 results, the topmost of them would match your needs.