Lol

I use the acronym LOL to respond to basically everything in online conversations. I may not truly be "laughing out loud" but it is a generic response that means a whole range of responses most of which would be non verbal markers. It sounds incredibly redundant and is very illustrative of how we attempt to include these non-verbal markers in our writings but some things just don't translate well.
"lol?" is used when there was the possibility of a joke, or they've said something that requires confirmation or clarification, as in "wait you're serious?"
"LOL" is when I actually did laugh out loud, LMFAO is reserved for when it was enough laughter to perform a spit-take at my computer monitor.
"lol" is when I'm not sure what to say, but I want to indicate that I'm still reading and paying attention, which would be non-verbally indicated by a head tilt, nodding or another change in position.

Something that is also common among my friends and I is the use of Astericks to set off actions, or example *shrug* or *Hugs!* there is also the interesting aspect of chat rooms run on an IRC server because they involve the command line /me which sets up for an action, an example of this is /me pounces nightwolf or /me throws a trout at spacemonkey those lines of chat are usually highlighted or offset slightly and help to make actions a little more noticeble and "realistic"

None of these gestures really translate well, because we miss the whole range of describing shapes and motions with your hands as well as expressions the speaker may not even realize they are making

-Missy Isaacs