Even easier, you can do EG Ctrl+Shift+^, then e, or Ctrl+', then e for the one with the apostrophe on top. It's not seeming to work on the reply box, but I found a quick reference. Works in normal text editors.
[TABLE="width: 420"]
[TR]
[TD="width: 138, bgcolor: #00007F"]
To produce
[/TD]
[TD="width: 256, bgcolor: #00007F"]
Press
[/TD]
[/TR]
[TR]
[TD="width: 138"]
à , è, ì, ò, ù
À, È, Ì, Ò, Ù
[/TD]
[TD="width: 256"]
Ctrl+` (accent grave), the letter
[/TD]
[/TR]
[TR]
[TD="width: 138"]
á, é, Ã, ó, ú, ý
Ã, É, Ã, Ó, Ú, Ã
[/TD]
[TD="width: 256"]
Ctrl+' (apostrophe), the letter
[/TD]
[/TR]
[TR]
[TD="width: 138"]
â, ê, î, ô, û
Â, Ê, Î, Ô, Û
[/TD]
[TD="width: 256"]
Ctrl+Shift+^ (caret), the letter
[/TD]
[/TR]
[TR]
[TD="width: 138"]
ã, ñ, õ
Ã, Ñ, Õ
[/TD]
[TD="width: 256"]
Ctrl+Shift+~ (tilde), the letter
[/TD]
[/TR]
[TR]
[TD="width: 138"]
[/TD]
[TD="width: 256"]
Ctrl+Shift+: (colon), the letter
[/TD]
[/TR]
[TR]
[TD="width: 138"]
Ã¥, Ã…
[/TD]
[TD="width: 256"]
Ctrl+Shift+@, a or A
[/TD]
[/TR]
[TR]
[TD="width: 138"]
æ, Æ
[/TD]
[TD="width: 256"]
Ctrl+Shift+&, a or A
[/TD]
[/TR]
[TR]
[TD="width: 138"]
[/TD]
[TD="width: 256"]
Ctrl+Shift+&, o or O
[/TD]
[/TR]
[TR]
[TD="width: 138"]
ç, Ç
[/TD]
[TD="width: 256"]
Ctrl+, (comma), c or C
[/TD]
[/TR]
[TR]
[TD="width: 138"]
ð, Ã
[/TD]
[TD="width: 256"]
Ctrl+' (apostrophe), d or D
[/TD]
[/TR]
[TR]
[TD="width: 138"]
ð, Ã
[/TD]
[TD="width: 256"]
Ctrl+' (apostrophe), d or D
[/TD]
[/TR]
[TR]
[TD="width: 138"]
ø, Ø
[/TD]
[TD="width: 256"]
Ctrl+/, o or O
[/TD]
[/TR]
[TR]
[TD="width: 138"]
¿
[/TD]
[TD="width: 256"]
Alt+Ctrl+Shift+?
[/TD]
[/TR]
[TR]
[TD="width: 138"]
¡
[/TD]
[TD="width: 256"]
Alt+Ctrl+Shift+!
[/TD]
[/TR]
[TR]
[TD="width: 138"]
ß
[/TD]
[TD="width: 256"]
Ctrl+Shift+&, s
[/TD]
[/TR]
[/TABLE]
Note that in the above shortcuts, unlike many of the others, you get a different symbol depending on whether the combining letter is capital or lowercase.
Source