I've tested 5 browsers. The test was to open list of 12 sites at the same time (each site in the tab). The sites are quite regular - en.wikipedia.org/wiki/Walmart, microsoft.com/en/us/default.aspx, ru.wikipedia.org/wiki/Израиль, etc... The below is Web browser memory usage.
Opera 9.64 - 92Mb
Firefox 3.5 - 105Mb
Safari 4 Beta (528.17) - 122Mb
IE 8.0 - 212Mb
Chrome 2.0.180 - 242Mb

*Switching to Firefox*