static void Main(string[] args)
        {
            string[] Sample = new string[] { "0", "1", "2", "3", "4", "5","6","7","8","9","a","b","c","d","e","f","g" };
            List<string> SampleList = new List<string>();
            SampleList.AddRange(Sample);
            List<string> result = getCombination(SampleList, 3);
            Console.Read();
        }
        static List<string> getCombination(List<string> SampleList, int m)
        {
            if (m == 1)
            {
                return SampleList;
            }
            List<string> result = new List<string>();
            if (SampleList.Count == m)
            {
                StringBuilder temp_sb = new StringBuilder();
                foreach (string s in SampleList)
                {
                    temp_sb.Append(s);
                }
                result.Add(temp_sb.ToString());
                Console.WriteLine(temp_sb.ToString());
                return result;
            }
            string temp_firstelement = SampleList[0];
            SampleList.RemoveAt(0);
            List<string> temp_samplist1 = new List<string>();
            temp_samplist1.AddRange(SampleList);
            List<string> temp_list1 = getCombination(temp_samplist1, m - 1);
            foreach (string s in temp_list1)
            {
                result.Add(temp_firstelement + s);
                Console.WriteLine(temp_firstelement + s);
            }        
            List<string> temp_samplist2 = new List<string>();
            temp_samplist2.AddRange(SampleList);
            List<string> temp_list2 = getCombination(temp_samplist2, m);
            result.AddRange(temp_list2);            
            return result;
        }
    }
}

------解决方案--------------------
int[] data = { 1, 2, 3, 4 };
var query = from a in data
           from b in data
           select a.ToString() + "," + b.ToString();
foreach (var item in query)
{
   Console.WriteLine(item);
}

------解决方案--------------------
http://www.cnblogs.com/rogerwei/archive/2010/11/18/1880336.html

------解决方案--------------------
写一个通用的：
IEnumerable<IEnumerable<T>> Combo<T>(IEnumerable<<IEnumerable<T>> source, IEnumerable<T> data)
{
   return data.SelectManay(x => source.Select(y => y.Concat(new T[] { x })));
}

------解决方案--------------------
C# code

        int[] data = { 1, 2, 3, 4 };
        private void SetData(int start,int count)
        {
            if (start == count - 1) return;
            for (int i = start+1; i < count; i++)
            {
                Debug.WriteLine(data[start].ToString() + "," + data[i].ToString());
                listBox1.Items.Add(data[start].ToString() + "," + data[i].ToString());                
            }
            SetImage(start + 1, data.Length);
        }

使用
SetData(0, data.Length);

/*
1,2
1,3
1,4
2,3
2,4
3,4
*/