memstats lists processes by memory usage (and not by CPU usage like top).

It reads information from /proc/PID/stat and /proc/PID/status, so it's very Linux dependant (sorry BSDs...).

output looks like "top" (because it's a good one).

soutade@cybelle> memstats
  PID    OWNER  VIRT   RES S       TIME         COMMAND
20098  soutade 3.10g 1.80g S   09:00:59         firefox
 1285     root  526m  259m S 6214:00:04            Xorg
 2555  soutade  862m  200m S 6214:00:10  gnome-terminal
 2113  soutade  827m  181m S 6214:00:20     gnome-panel
20081  soutade  866m  153m S   10:00:12     thunderbird
 2122  soutade 1.97g   98m S 6214:00:20        nautilus
 2192  soutade  591m   86m S 6214:00:13 indicator-apple
20104  soutade 1.07g   42m S   09:00:58          pidgin
26536  soutade  627m   40m S   06:00:22           gedit
 6517  soutade  529m   30m S 2816:00:40           emacs
 2845  soutade  442m   27m S   00:00:50           emacs
22935  soutade  449m   23m S  103:00:06           emacs
 2094  soutade  899m   23m S 6214:00:21        metacity
 2207  soutade  393m   11m S 6214:00:13 indicator-messa
 2762  soutade  114m   10m S   00:00:48          python
 9752  soutade  401m    8m S   96:00:18 gnome-screensav
 2070  soutade  766m    7m S 6214:00:22 gnome-settings-
 2914  soutade   94m    6m R   00:00:00        memstats
 2121  soutade  477m    6m S 6214:00:20 notification-da
 2489  soutade  414m    6m S 6214:00:20 update-notifier
23305  soutade  391m    5m S 5641:00:44 ubuntuone-syncd
 2280  soutade  418m    4m S 6214:00:10 gdu-notificatio
 2061  soutade   22m    4m S 6214:00:22     dbus-daemon
 1973     root  192m    4m S 6214:00:32         lightdm
 6886  soutade  581m    4m S 3797:00:46 gnome-keyring-d
 2134  soutade  539m    4m S 6214:00:19 gnome-fallback-
28423  soutade   85m    4m S   05:00:43            bash
 2389  soutade  335m    4m S 6214:00:00 zeitgeist-daemo
 6080  soutade  332m    4m S 3624:00:44      pulseaudio
 2382  soutade  400m    3m S 6214:00:00 zeitgeist-datah