calculator applet for GNOME panel: wcalc-applet-0.2.tar.gz
color picker applet for GNOME panel: wpicker-applet-0.1.tar.gz
both applets are written in python.
please note: i've already moved to xfce4 because of news that GNOME going to depend on Mono project (i don't want mono or anything .net/ms related on my computer), so there will be no new/improved versions of those applets.
you can expect to see xfce4 versions of these applets soon, when i'll get some time to figure out xfce4 python bindings.
for now, you can use "xfce4-xfapplet" package to load GNOME applets in xfce4 panels.