Warning: C++ is not C and the following is related only with C++.
If you are already a c# developer I think you should work in three different directions:
1) copy semantic, memory management and const keyword, these are the main differences between c# and c++.
Make yourself familiar with copy constructor, destructor and assignment operator. Learn how to use RAII idiom.
Study the differences between passing a variable by: value, reference and pointer.
I will suggest Effective C++ http://www.amazon.com/Effective-Specific-Improve-Programs-Designs/dp/0321334876 also guru of the week it is a great source.
In More Effective C++ there is a nice chapter on the difference between pointer and reference.
2) you need to make yourself familiar with the standard library, in my opinion this is a really good book http://www.amazon.co.uk/Standard-Library-Tutorial-Reference/dp/0201379260/ref=sr_1_4?ie=UTF8&qid=1314957062&sr=8-4
3) the standard library is great but not enough, you will soon need boost.
I am reading this book at the moment http://www.amazon.co.uk/Beyond-Standard-Library-Introduction-Boost/dp/0321133544/ref=sr_1_1?ie=UTF8&qid=1314957541&sr=8-1
I haven't finished it yet, but it looks good so far.
Keep practise, you are going to love coding in c++.