One, two, three, four abreast according to device width.
inline:block divs (centered or left-align), constant height
1 on ipod / sony smartphone (up to 640 pixels wide)
2 on samsung tab 8 (up to 980 pixels wide)
3 on toshiba 15" laptop (up to 1400 pixels wide)
4 on desktops wider than 1400 pixels