If your computer has a "character map" accessory or utility (or perhaps "character set") this will fairly easily give you the numerical codes for the "alt" approach Bob Bolton is talking about.

Here are some of the more useful ones at least when writing to and from American computers. (Somebody tell me if any of these don't work with normal Western European character sets. People using other keyboards or character encodings, or who have selected oddball fonts as their defaults will likely not see a lot of these as intended, at least if you use the "alt" method.) —

Bob Bolton already gave you
é (e acute) Alt+0233
Here are some others:
€ £ ¥ (euro, pound & yen symbols) Alt+0128, Alt+0163 & Alt+0165
' ' (left and right single quotes) Alt+0145 & Alt+0146
" " (left and right double quotes) Alt+0147 & Alt+0148
• (a fairly substantial buller) Alt+0149
– — (en-dash and em-dash) Alt+0150 & Alt+0151
¡ ¿ (Spanish inverted exclamation and question marks) Alt+0161 & Alt+0191
© ® ™ (copyright, registered trademark, trademark) Alt+0169, Alt+0174 & Alt+0153
Ich weiß nicht (German s-z ligature = ss) Alt+0223
à la carte (a grave) Alt+0224
Bogotá (a acute) Alt+0225
São Paulo (a tilde) Alt+0227
Handel (né Händel) (a umlaut) Alt+0228
Blessèd art thou (e grave) Alt+0232
moi-même (e circumflex) Alt+0234
the Brontë girls ("e umlaut", a misnomer) Alt+0235
façade (c cedilla) Alt+0231
Encyclopædia Britannica (a-e ligature) Alt+0230
Loftleiðir (Icelandic airline) (edh) Alt+0240
Così fan tutte (i grave) Alt+0236
Líolaind is my name in Gaelic guise (i acute) Alt+0237
naïveté ("i umlaut") Alt+0239
piñata (n tilde) Alt+0241
Ramón (o acute) Alt+0242
Köln (German for Cologne) (o umlaut) Alt+0246
Købnhavn (Danish for Copenhagen) (o slash) Alt+0248
Gesù Bambino (u grave) Alt+0249
Búsqueda en Google (u acute) Alt+0250
17 août 1851 (u circumflex) Alt+0251
Deutschland über alles (u umlaut) Alt+0252
etc. etc.
I'm getting carried away. "Umlaut" is a misnomer for the two dots over some vowels; technically these are called a "diaresis" (plural diareses), and umlaut refers to the kind of vowel sound that the diaresis usually signals in German and some other languages (e.g. Finnish). Capital letters are also available, starting with Àine (Alt+0192) and ending with Vilhjálmur Þ. Vilhjálmsson (Alt+0222). Here's a link that shows the ones that are not accented letters (plus a couple of the accented letters) in case you haven't been able to find your Character Map: ASCII chart tutorial. Remember that the extended ASCII character set was designed primarily to allow Americans (and the odd stray Englishman) to communicate electronically with our cold-war-era NATO allies, hence the accommodation of Icelandic at the expense of, say, Polish or Hungarian. Of course, lacking Turkish letters like ğ, it was really only good for the Northern and Western European allies, but still, it proved quite popular. (I'm guessing about the history of ASCII, doing it off the top of my head, not on any documentary basis.)

It's getting late. I'm rambling. Hope some of that helps somebody.

Liland