[b][/b] bolds things: b
[i][/i] puts things in italics: i
[size=num][/size] changes text size to num: size
[color=clr][/color] changes text color to clr: color
[glow=color][/glow] glows things in color:

glow

[alpha=number][/alpha] makes things transparent number is how visible(%) great for smilies:

alpha

[spoiler=clr][/spoiler] makes things readable only by selecting them by making the bg and fg colors both clr:

spoiler

Put a [color=black][/color] inside [spoiler=clr][/spoiler] to make normal text with a colored bg:

spoiler+color

Putting them together can make some great effects
--WetWired