I looked in the Corpus of Contemporary American English (COCA), and the British National Corpus (BNC), and found this data:
COCA:
1 JUDGMENT 15116
2 JUDGEMENT 584
Ratio in American usage: 25 to 1 in favor of judgment
BNC:
1 JUDGMENT 3220
2 JUDGEMENT 2441
Ratio in British usage: 1.3 to 1 in favor of judgment
So, it does appear that while judgment is more common in both British and American English, judgement enjoys a substantial percentage of usage in British English, but much less in American English.
Addendum: per ShreevatsaR’s suggestion, I searched the BNC again, this time excluding all the spoken sections (“S_*”) as well as the two written legal sections: “W_nonac_law”, “W_ac_law_edu”, and got these results
1 JUDGEMENT 2053
2 JUDGMENT 1317
We do now find the numbers inverted: the ratio of judgment to judgement is just 0.64. Although many of the examples remaining of judgment are in fact in a legal context anyway, we do find, though, that the spelling judgment nevertheless enjoys considerable usage in non-legal contexts. Here are a few examples:
- “Efficiency at work is decreased and judgment impaired, with possible serious results.”
- “There I had him as a charming, affectionate colleague of mature judgment.”
- “It is not pleasant for a human being to pass judgment on another and say that he is evil through and through without any redeeming features”
- “Judgment of humorous writing is even more subjective than with any other kind.”
Let's take them in reverse order:
I work today.
This means that you are going to work today. It is not said if you are currently working. Examples would be:
I can't go to the beach. I work today.
Aww, the boss screwed my day off. I work today, but at least I have tomorrow off.
Now, this is still not what most native speakers would say. They would probably say "I have work today," or "I'm working today." Which brings us to your first example:
I am working today.
This will mostly be used when you mean that you are going to work today. It can also be used if someone asks you what you're doing while you are at work (or on a lunch break). It would not normally be heard at work, because it should be obvious to any questioner who is present that you are working (and if it's not obvious that you are working, any question about what you are doing would be intended as a rebuke). The most common use case would be if you got a call on your cell from a friend:
Caller: Hey, what are you up to? I thought we could grab some beer and hit the beach.
You: I can't. I'm working today. Can I get a raincheck?
EDIT
You may also get some use out of looking at this question and answer, which I helped craft (along with some of the EL&U moderators and other bright lights on this site). It's not perfect, and it's still a work in progress, but we designed it to give non-native speakers a visual introduction to what the statements of time mean in English.
Best Answer
There are a small number of words aside from ageing that retain silent e before -ing; for some of them, this spelling is mandatory in American English as well as British English. For others, it is optional in both of these varieties of English. Retained silent e before ing seems to occur mainly after vowel letters (including y) or after the letter g, especially in the sequence nge.
Of course an e cannot be dropped when it is used as a single letter to represent a vowel sound directly before the suffix -ing, as in being or the trisyllables segueing, sauteing (or sautéing) and appliqueing (or appliquéing).
The digraph ee also retains both letters before -ing (seeing, freeing, decreeing), even though one e is lost as a rule when -ee comes before a suffix that starts with e such as -ed, -er, -est.
It is standard to drop the letter e that is used after the letter l or r to indicate a syllabic liquid or a sequence of schwa + liquid: rambling, massacring, and in British English centring, manoeuvring.
Mandatory
Two important mandatory examples: dyeing (not dying), singeing (not singing). Dropping the e in these words would cause ambiguity with the -ing forms of die and sing respectively.
Verbs ending in -oe also seem to mandatorily keep the e (-oeing):
This doesn't avoid any lexical ambiguity as far as I can tell, but perhaps helps indicate that they are not pronounced with the diphthong usually represented by oi, as in the onomatopoeia boing. Going and doing exist despite this, however.
This is complicated a bit by the existence of an alternative spelling sorty, which means that sortying is also a valid form. However, I haven't found any source that supports a paradigm like sortie, sorties, sortying. The same applies to stymie, as far as I can tell. At any rate, it's clear that the gerund/present participle form of a verb ending in -ie is generally not spelled with -iing.
This is a rare word meaning "prophesying", from Scots. There are probably other Scots verbs ending in -ae that have some use in English. All of the dictionaries I've consulted that list inflections for this word in modern English show it as retaining the e in its -ing form.
Optional
Retaining the "e" is optional for some verbs.
Ending in consonant sounds:
-nge pronounced as /nd͡ʒ/: tingeing, twingeing, bingeing, whingeing, swingeing*
*I think the e of swingeing is usually kept to distinguish it from swinging, the -ing form of swing, but the AHD indicates that the e may be dropped anyway. The word swinge is used more in British English than in American English.
-gue pronounced as /g/: rogueing, vogueing
-ge pronounced as /ʒ/: lugeing
Ending in vowel sounds:
-(e)ue pronounced as stressed /(j)uː/: queueing†, blueing‡, rueing, cueing, sprueing (the last is uncommon, so it's in the OED but not in any free online dictionary that I know of)
However, the verb value, where "ue" represents an unstressed vowel, always drops the "e" before -ing: valuing
†There is also an ELU post on "Queueing" or "Queuing"
‡Some people may consider "blueing" a misspelling; see the comments in Why are 'blueish' and 'bluish' both considered correct spellings?
eye pronounced as /aɪ/: eyeing
Questionable
-ie pronounced as /aɪ/: vieing? This looks very odd to me, and no major modern online dictionary lists it, but there are a small number of more-or-less contemporary examples from Google Books and from online sources (for examples, see Vocabulary.com and wordnik): these can probably just be regarded as misspellings, although they cannot be dismissed as typos because there are sources that use this spelling consistently (such as Social Ontology: Recasting Political Philosophy Through a Phenomenology of Whoness, by Michael Eldred).
the extremely rare inoneing, listed in the OED with two citations, from "in-" + "one" or the phrase "in one". Obviously one has a very non-standard pronunciation for a word ending in the letters "one".
"routeing", mentioned by Muzer in a comment:
(Also see "Skyping or Skypeing".)
Nonstandard
There are also a number of more or less common nonstandard spellings/misspellings with this feature, such as "battleing" (for standard "battling"). The variability in people's intuitions about whether to include a silent "e" here seems similar to to the variability before the suffixes "-able", "-ish", and "-y".
Examples compiled with the help of Onelook wildcard search and tchrist's post in chat.
I think there are better/more complete descriptions in many sources about English; you could probably find some on Google.