After having to add dollar signs and format SI units countless times in the review section on Physics, I finally got fed up and wrote a script.{*}
It basically adds buttons/keyboard shortcuts to enclose the selected text in dollar symbols. (it does more, but that functionality is hidden for math.SE)
It's pretty useful in /review, and also a good shortcut when writing your own posts.
Here's the userscript. Installation instructions are there. (also bugs/feature reqs/whatever)
*With some urging from chem.SE.people, otherwise it was going to be indefinitely in my todo list :P