Okay, inspired by problems many non-French people here seem to have, I'm here to help!
So, I actually went through Wikipedia looking for codes that everyone can use (at least on html-based sites) whatever their keyboard happens to look like.
Firstly: In the case of all of these codes: Remove the spaces! The & and ; should not be separated from the main code text.
1: Çç or C-cedilla
& Ccedil ; -> Ç
& ccedil ; -> ç
Examples:
"Ça va?"
"Français"
Pronounced like an s.
2: Éé or E-acute
& Eacute ; -> É
& eacute ; -> é
Examples:
"chéri/chérie"
"café"
Pronounced something like "eh" (close e).
3: Èè or E-grave
& Egrave ; -> È
& egrave ; -> è
Examples:
"frère"
"chère"
"très"
Pronounced like e in "bed" (open e).
4: Àà or A-grave [NOTE: French only has a-grave, so no a-acute.]
& Agrave ; -> À
& agrave ; -> à
Examples:
"voilà"
"à la"
"déjà vu" [see how the e has an acute accent while the a has a grave accent]
Pronounced like a in "father".
5: Ëë or E-umlaut
& Euml ; -> Ë
& euml ; -> ë
Examples:
"Noël"
Pronounced like è. (Or like e in "bed".)
6: Ïï or I-umlaut [This is a pretty rare one but you occasionally see it... at least in names and such]
& Iuml ; -> Ï
& iuml ; -> ï
Examples:
"maïs"
"Loïc" (a name)
Pronounced like ee in "see".
7: Circumflex (âêîôû) [Actually I don't remember ever seeing û in French but I'm putting it there along with the others.]
& acirc ; -> â
& ecirc ; -> ê
& icirc ; -> î
& ocirc ; -> ô
& ucirc ; -> û
Examples:
"pâte"
"fête"
"s'il vous/te plaît"
"hôtel"
Hope this helped someone. =3=b And hope I didn't mess anything up...