Let us not forget the “!” exclamation mark, which I believe is used to represent a clicking sound in certain African tribal languages, such as that spoken by the !Kung. I think English, and languages in general could stand to have more clicking.
>> The Spanish alphabet inlcudes “ll”, “ch”, “rr” and other sounds outside our 26 letters
All three are not currently in the Spanish alphabet one has to learn by heart in elementary school. In fact, I never had to learn where to put “rr” in the alphabet, and when I was leaving elementary school, they changed the alphabet to banish “ll” and “ch”. There is still a case made to include the “ch” sound in the alphabet, but I do not know much about it. The only character that remains (and will remain) is the “ñ” sound.
Here is an excellent article about the choosing of an alphabet, and the letters in it, in post-Soviet Azerbaijan.
I don’t see any new letters being added any time soon. The alphabet has been static for 900 years – since the beginning of Middle English-and even before that only thorn and a couple of other letters, which I think were merely inherited from Indo-European language, were ever in our alphabet. Frankly I’m glad that we don’t still write like “þaet dole bearn,” (that foolish child) not only because OE adored the subjunctive and all its tenses, but because symbols the thorn are hard to draw; would the “new letters” be any less complex? All the simple shapes are already used. Anyway, I think our alphabet covers all the sounds we use when properly pronouncing words.
It’s associated with several vowels because in American English, pretty much any vowel in an unstressed syllable becomes a schwa. That tendency and the fact that the schwa is kind of in the middle of the vowel space is why it’s sometimes called the “sinkhole” vowel.
The reason you probably wouldn’t want to use the schwa in spelling is because it would introduce complexity without being particularly useful. Sometimes adding suffixes or prefixes to a word changes the stress pattern, and unstressed vowels become stressed or vice versa. So the schwas come and go. Some English words have morphological schwas, but far more gain them from prosody, which could change.
Generally speaking, reflecting this change in spelling would be overly complicated, plus we’d have to change the spelling every time there was a shift in pronounciation. Also different dialects of English would spell things differently.
I’m not saying our spelling system is that great right now, but too much adherence to phoenetics isn’t necessarily a good thing.
-fh
In the early Pre-Cambrian age before Windows, when most monitors displayed 80 columns of text and most people had 9-pin dot matrix printers, the Print Screen button actually did send the text directly to your printer. Since Windows became near-universal, it now sends a copy of your screen to the Windows cut&paste buffer. You can paste it into Paint, or other programs that support graphic data. Also, Alt-Print Screen will copy just the active window.
If you ask me, the choice to use [schwa] for the most common letter in the Azerbaijani alphabet was one dumbass numskull move. I actually write a little in Azerbaijani, but I cannot make a schwa in Unicode that will come through here or anywhere else. The schwa is not necessarily an easy character to find if you’re a printer. Whereas the ä character is easy for anyone with a computer to make anywhere. Also, the phonetic value of schwa as the neutral central vowel is well-established; the Azerbaijani vowel is low-mid-front (the sound of a in English cat or hat); the use of ä for this vowel is conventional, especially by Turkic scholars. Come on, Azerbaijanis: maybe it isn’t too late to rethink this blunder.
What the heck is the “Scroll Lock” key doing there, anyway? Why do keyboard manufacturers keep sticking this utterly useless key on there?
I remember using DOS programs where you would use the scroll lock key to lock the cursor in place so you could use the arrow keys to scroll up and down in a document without moving the cursor. Now we have a scroll bar on screen, but remember… not everybody uses a GUI.
As for getting rid of it, a tiny percentage of computer users probably still need a scroll lock key (at my temp jobs I’ve used any number of ancient DOS-based programs which used all kinds of funky keys), and removing it would make their software inoperable. If you don’t need it, it isn’t hurting you. Type around it 
-fh
We already have three new letters of the alphabet: @ . and /
At least, I see 'em everywhere and they’re not punctuation.
unless someone has already said this, a good one for ‘th’ is like a ‘h’ but the | part is crossed, so it is like a ‘t’ with the hooky part of the ‘h’
I agree about emoticons being the next step in our language. The problem of extra keys is even solved by the way many programs translate into a little picture of a smiley face. The smiley is also useful. I sometimes have to remind myself not to add it to papers and stories for school.
The Welsh language treats Ch, Ng, Ph and Th as separate letters (called ech, eng, ffi and eth, respectively). As far as I can tell, it makes no difference whatever to pronunciation or orthography.