Well, I think Opera (not quite a hundred tabs, I think) takes about 1.5G by itself.
There's some two dozen icons in the systray, so Steam's running, Trillian with hald a dozen IRC channels, Foobar 2k with a bunch of medium long playlists, Mahogany mail client, two terminals, a DNS server, AD server, DHCP server, a few picture viewer and explorer windows, NFS client, possibly ASUS AI suite, nvidia, realtek, asus xonar, logitech, intel storage driver front ends, daemon tools,
Pretty normal, except for some of the server stuff, I guess. Still, most of the memory is being used for caching, (around 2.5GB) so I don't complain. Actual "bound memory" by applications and system is probably around 2.5GB? Not at that machine right now, so can't check.
Double check the four-line summary (total/caches/available/free) on your machine. It shouldn't have more than 500MB free or something is wrong. The amount of 'available' memory is what makes your machine feel fast. The more memory is available, the more memory is used by applications while also being in the page file. Once you request more memory than is 'free' some of the stuff from the 'available' pool will be dropped, and if you resume the other application will have to be loaded from disk. That's what often slows down a machine. Not as noticeably as when you completely run out of memory, but depending on the severity it can still be pretty bad.