I have Microsoft Word's rather handy grammar checker on, but if I use an abbreviation or a word like "Yahoo!" Word marks the punctuation as the end of the sentence, and then marks the uncapitalized next word as a grammar error because it thinks that is the start of a sentence. Is there any way to fix this?
If it is only a couple of abbreviations of brand names (Yahoo!) that you keep coming across, then you can add them to the AutoCorrect exceptions for "do not capitalize after:"
In Word 2007 click the Office Orb button and choose Word options or in 2010 click File then Options
I'm not sure about 2007 but in 2010 you're looking for the AutoCorrect options under Proofing.
On a side note there should already be a substantial list of abbreviations, assuming they are enabled.