Most Thai Forest teachers focus on anapanasati; the greatest of them all, in my mind, was Buddhadasa Bhikkhu.
Check out A Manual for Serious Beginners: http://what-buddha-taught.net/Books3/Bh ... athing.htm
It's important to note that most Thai Forest Teachers don't break up samatha and vipassana meditation into separate groups; like the Buddha himself, they teach Jhana, in which both insight and concentration are developed together.
Gain and loss, status and disgrace,
censure and praise, pleasure and pain:
these conditions among human beings are inconstant,
impermanent, subject to change.
Knowing this, the wise person, mindful,
ponders these changing conditions.
Desirable things don’t charm the mind,
undesirable ones bring no resistance.
His welcoming and rebelling are scattered,
gone to their end,
do not exist.
- Lokavipatti Sutta