^ Don't think you can get away with having an LLB in the States unfortunately... JD's are the in thing in the US at the moment...
you can most certainly practice in all countries of the Commonwealth that have inherited the UK system of Common Law... eg: Singapore, Hong Kong (big money!!!!), Canada, etc...
think you would need to do some form of bridging course if you wish to practice elsewhere... (don't hold me to this one, its best you talk to a representative in the area where you would wish to pursue admission; or maybe even the university you are applying for...)
There's also international opportunities where you may be able to use your legal qualifications on the world stage... eg: United Nations, International Court of Justice, International Criminal Court (need to be the creme de la creme for these institutions... being well respected, intelligent, coming from a school which is internationally recognised, lots of experience, etc is an absolute must)
I had a lecturer from the US for one of my summer subjects, so I am assuming that it is applicable... However, this individual was very, very well educated... (Phd well educated...)