So I found this mod that I now got installed in my 1.4.2 jar file, it is a mod that gives you this fairly small little GUI, it shows the durability on your armor if you got any armor on, if you are holding your tool/weapon (Yes you need to hold it) it also shows the durability for that, if you are holding a item it shows the amount you are holding of the item (1 - 64)
Screenshot (You see the GUI in the right lower corner)

If it is allowed I suggest you download it, very simple to download (Only two files) or if you use MultiMC just drop it in! :)
REMEMBER: you need Forge Modloader or Normal Modloader I use Forge cause it is
the best in my opinion :)