LLM Guide has an interesting topic on this subject:

http://www.llm-guide.com/article/149/summer-law-programs

Does anyone know any ranking regarding these courses?

I'm considering going to the USA a couple of months before in order to enroll in one of these programs.

Does anyone have any thoughts to share on this?

I read the same article some time ago with great interest! If admitted to a US law school, I was thinking of doing a pre-LLM summer course in London. What about you? Are you also applying to US law schools?

If I am accepted I intend attend a pre course in the same city where I'll attend the LLM.
Which LLM programs did you guys apply to?

NYU and UF - International Taxation
GULC - Taxation

And you?

HLS
Stanford
Berkeley
Columbia
Georgetown

Any idea on how it would work with regards to VISA issues?