Writing FizzBuzz

I think your implementation is unnecessarily complex. This one does the job and is easier to understand:

public void DoFizzBuzz()
{
    for (int i = 1; i <= 100; i++)
    {
        bool fizz = i % 3 == 0;
        bool buzz = i % 5 == 0;
        if (fizz && buzz)
            Console.WriteLine ("FizzBuzz");
        else if (fizz)
            Console.WriteLine ("Fizz");
        else if (buzz)
            Console.WriteLine ("Buzz");
        else
            Console.WriteLine (i);
    }
}

I think what you're trying to accomplish is a generic solution to FizzBuzz, that will work for any number of number-word combinations.

You have a good start - I think I can answer your questions with this example:

public void DoFizzBuzz()
{
    var combinations = new List<Tuple<int, string>>
    { 
        new Tuple<int, string> (3, "Fizz"), 
        new Tuple<int, string> (5, "Buzz"), 
    };

    Func<int, int, bool> isMatch = (i, comb) => i % comb == 0;
    for (int i = 1; i <= 100; i++)
    {
        Console.Write(i);

        var matchingCombs = combinations.Where(c => isMatch(i, c.Item1)).ToList();
        if (matchingCombs.Any())
        {
            Console.Write(string.Join("", matchingCombs.Select(c => c.Item2)));
        }
        else
        {
            Console.Write(i);
        }
        Console.Write(Environment.NewLine);
    }
}

In practice, you would pass combinations in to the method, but I included it inside just to be concise.

Take advantage of conditional format specifiers to get a nicely golfed version:

public void DoFizzBuzz()
{
    for(int i=1;i<101;i++)Console.WriteLine("{0:#;}{1:;;Fizz}{2:;;Buzz}",i%3*i%5==0?0:i,i%3,i%5);
}

Unrolled for maximum efficiency. This program can outfizzbuzz all others.

public void FizzBuzz()
{
    const string FIZZ = "Fizz";
    const string BUZZ = "Buzz";
    const string FIZZBUZZ = "FizzBuzz";

    int i = 0;
    while (i < 150)
    {
        Console.WriteLine(++i);
        Console.WriteLine(++i);
        Console.WriteLine(FIZZ); ++i;
        Console.WriteLine(++i);
        Console.WriteLine(BUZZ); ++i;
        Console.WriteLine(FIZZ); ++i;
        Console.WriteLine(++i);
        Console.WriteLine(++i);
        Console.WriteLine(FIZZ); ++i;
        Console.WriteLine(BUZZ); ++i;
        Console.WriteLine(++i);
        Console.WriteLine(FIZZ); ++i;
        Console.WriteLine(++i);
        Console.WriteLine(++i);
        Console.WriteLine(FIZZBUZZ); ++i;
    }
}