For what it is worth, wiki cites several respected typography and style guides, including the “Chicago Manual of Style” and the “Oxford Style Manual” (aka Hart’s Rules) and they agree on single space:
With the advent of the computer age, typographers began deprecating double spacing, even in monospaced text. In 1989, Desktop Publishing by Design stated that “typesetting requires only one space after periods, question marks, exclamation points, and colons”, and identified single sentence spacing as a typographic convention.[34] Stop Stealing Sheep & Find Out How Type Works (1993) and Designing with Type: The Essential Guide to Typography (2006) both indicate that uniform spacing should be used between words, including between sentences.[35]
More recent works on typography weigh in strongly. Ilene Strizver, founder of the Type Studio, says, “Forget about tolerating differences of opinion: typographically speaking, typing two spaces before the start of a new sentence is absolutely, unequivocally wrong.”[13] The Complete Manual on Typography (2003) states that “The typewriter tradition of separating sentences with two word spaces after a period has no place in typesetting” and the single space is “standard typographic practice”.[36] The Elements of Typographic Style (2004) advocates a single space between sentences, noting that “your typing as well as your typesetting will benefit from unlearning this quaint [double spacing] Victorian habit.”[6]
David Jury’s book, About Face: Reviving the Rules of Typography (2004)—published in Switzerland—clarifies the contemporary typographic position on sentence spacing:
Word spaces, preceding or following punctuation, should be optically adjusted to appear to be of the same value as a standard word space. If a standard word space is inserted after a full point or a comma, then, optically, this produces a space of up to 50% wider than that of other word spaces within a line of type. This is because these punctuation marks carry space above them, which, when added to the adjacent standard word spaces, combines to create a visually larger space. Some argue that the “additional” space after a comma and full point serves as a “pause signal” for the reader. But this is unnecessary (and visually disruptive) since the pause signal is provided by the punctuation mark itself.[37]
…
..style guides began changing their guidance on sentence spacing. The 1969 edition of the Chicago Manual of Style used em spaces between sentences in its text;[41] by the 2003 edition it had changed to single sentence spacing for both manuscript and print. By the 1980s, the United Kingdom’s Hart’s Rules (1983)[42] had shifted to single sentence spacing. Other style guides followed suit in the 1990s.[43] Soon after the beginning of the 21st century, the majority of style guides had changed to indicate that only one word space was proper between sentences.
— http://en.m.wikipedia.org/wiki/Sentence_spacing
That’s good enough for me. 😀