These shorthand expressions are known as smileys or emoticons. They're easy to figure out once you get the hang of it. Just remember that they're all sideways faces. See Table 1 for a list of the most commonly used emoticons. There are whole books about smileys for those who are interested, including the enjoyable Smiley Dictionary by Seth Godin.
People also use abbreviations to express emotional states or to qualify what they're saying.
See Table 2 for a list of common abbreviations. Then rant away. But when you're communicating online, in most cases it's back to the typewriter as far as effects go. Even if your mail system lets you use boldface, italics, and tabs, there's no guarantee that your correspondent's system will understand them. At worst, your communication will turn into unreadable gibberish.