there are websites like Speedtest.net which tell you your internet speed in one minute , but you cant visit them 10 times a day , to check your internet speed ,you need to see in realtime.

Netspeed is a GNOME-applet that shows how much traffic occurs on a specified network device ( ethernet ,Lan network, dial up modem or even a sat card ) and you can see in realtime, what is going on with your internet download and upload speed .
I simply love it !
you can install it in three clicks :

1- Go to synaptic package manager and install it . (make sure universe repository is enabled)
2- Right click on your panel (at top) and choose "add to panel"
3- Find "network monitor" in the list and add it to your panel.
Quick tips :
- "Netspeed" can monitor many devices, make sure it shows the speed of the device which you want.
right click on the applet , then "preferences" , and choose your network device , eth0 , dial up or whatever...
- You can move its position on the panel . (right click on the applet , choose "Move")