Reddit mentions of Tai Chi Chuan: 24 & 48 Postures with Martial Applications

There's also /r/taijiquan (using the pinyin system for Chinese). I do personally like to read up, but a good instructor - or at least occasional clinic/camp style instruction is more or less a must.

It probably takes quite long to practice tai chi ch'uan to have fighting proficiency, but if that's your goal, doing something else as well and trying to apply the principles might be a shortcut. The practice of taiji could be roughly divided into three categories: First and most popular is health-oriented light calisthenics. (These often do drop the "ch'uan" or "fist" from the name of the art.) Second is "wushu", Chinese martial arts tricking ("wushu" means "martial arts", but these days it usually refers to the acrobatic sport). And third is traditional martial arts. The likelihood of finding someone with combat proficiency increases as you go down the list, but even if someone's doing "traditional tai chi" and can track his or her lineage back to the Chinese big shots, it's no guarantee of actual proficiency.

For the closest westerners can get to original sources, there's Paul Brennan's translations on old manuals. Do note, those aren't how-to manuals, but rather reference for someone who already knew the arts.

This book is a good introduction, IIRC. I'd need to check my library.

If you use Amazon's Kindle, Ken Gullette has a nice no-nonsense material on the Chen Xiaowang short form as well as the body mechanics. (Also runs an "online school" with video material.)

This book is a very comprehensive intro on the subject of Yang style taijiquan. This book is a good intro on one of the short forms, along with video sources to cross-reference, such as Ian Sinclair's YouTube series.