You could use any type of weapon if you want, but would it actually help you ? Personally I think our tanking weapons are lacking for ProtWarriors and ProtPallies.
It would be easier if I knew what type of tank you where, but I will just tell you what I did.
Important : An upgrade is an upgrade no matter how small it might seem.
As a ProtPally I had a hard time to get a nice tanking weapon, I did not see one that I could use until I started to do Dungeons Normal/Heroic. I would suggest to get a weapon with +Def, +Dodge, +Parry etc. This way you can ease up on the +Def, +Dodge on other gear slots with enchants and Gems and use STR STA ones.
In my quest for a better blade I came across the following site. (I am new to wow so my number crunching is not that great yet, so I use all resources available to me)
Raid Ready Check
It's simple to use, just put in your Realm Server Name. Then get the info it scales you on what you have and where you will get your better upgrades from.
The short would be,
Option 1 : Eternally Folded Blade
This is located in HoL normal (Halls of Lightning) and drops from the second boss, Volkhan. This I think was one of the 1st Tanking weapons I used. Although not great it does give you a boost for your tanking. For normal this was easy fight so it should not be difficult to get this one.
For me this was almost a sure drop everytime I did the run.
Option 2 : Infrantry Assaut Blade
This is located in UK Heroic (Utgarde Keep) and drops from the first boss, Prince Kelseleth. Very simply fight just burn him down. Break the ice tomb's if you do not want to go for achievement or have it already.
For me drop rate was 3 out of 7 runs.
Option 3 : Red Sword of Courage
This is located in UP Heroic (Utgarde Panicle) and drops from the last boss, King Ymiron. Once again fight was easy just stay away from the bubbles ^^. This is the must have for ProtPallies and Protwarriors before going to Raids as this is your last Heroic upgrade before you next one will come from Naxx.
Still trying to get it. ( Did the run 3 times now and saw it drop twice, 1st time with guild and they DE cause I was Ret Specced. Second time when I was tank the PUG DPS need rolled on it for his Alt specc and he got it QQ)
Drop rate 2 out of 3.
This is how I want to upgrade my pally, it might not work for you but it sure is working for me.
Hope this helps you I this is my plan for getting my tank ready. GLHF