In any system of meditation, one can categorize the techniques endlessly. One could divide them into active, passive, and waking, or make distinctions between mental, emotional, and physical meditations. Active meditation techniques require you to focus on some object to the exclusion of all else - like a meditating on a symbol, a set of words or an image. A passive meditation involves stilling the mind so that the train of thoughts which occupy our consciousness so pervasively stop. The surrounding world fades from immediate awareness. The bodies noises and impulses cease to grab our attention, until finally the mind holds "no- thing". Waking meditations consist of meditations one practices continuously. Like the exercises in mindfulness one finds in Buddhism.
Mental meditations have the purpose of developing the intellect. One might consider doing a logic puzzle or studying a foreign language a mental meditation, albeit a simple one. Emotional meditations explore the breadth and flavor of our emotions: for one cannot hope to control a thing without first understanding it. Physical meditations consist of various strenuous exercises done in a particularly mindful manner.
Vulcans use meditation for arie'mnu (mastery of passion and emotion), and training the mind for complex uses of the intellect. So the later method of categorization seems most suited to our exploration of the subject. All Classification aside, the most important thing about meditation remains that one does it - regularly and mindfully. Intermittent meditation practices lead to intermittent results.