Another vote for iStat Menus. It costs money, but it's my favorite and a bit superior to the open source alternatives like Stats, IMHO, which is somewhat influe

Another vote for iStat Menus. It costs money, but it's my favorite and a bit superior to the open source alternatives like Stats, IMHO, which is somewhat influenced by iStat Menus' design. (though I like Stats's graph view more). iStat has a very flexible customization system and pulls in more data then all the alternatives I've found. Stats for example doesn't show you the per-process disk activity like iStat Menus. I split a family license with a friend to save some $$.