1, str1.Equals(str2)
2, int result = string.Compare(str1，str2);
int result = string.Compare(str1，str2, true) //忽略大小写比较
3、在某些语言中，可以利用 >、=、< 来直接比较字符串，而在 C# 中，只能用 == 来比较两个字符串是否相等，更多的比较使用 CompareTo 方法。
语法
public int CompareTo(
string strB
)
返回值
小于 0，实例小于参数 strB；
0，实例等于参数 strB；
大于 0，实例大于参数 strB，或者 strB 是 null 引用。
示例
string strA = "abc";
string strB = "ABC";
int result = strA.CompareTo(strB);
备注
此方法使用当前区域性执行单词（区分大小写和区域性）比较。
http://blog.csdn.net/CaoJinGangLove/archive/2008/11/05/3227544.aspx
附录：
Console.WriteLine("*******************String.CompareTo()*********************");
String strTestCompare = "abc";
//strTestCompare.CompareTo("abc")=0
//strTestCompare.CompareTo("ab")=1
//strTestCompare.CompareTo("a")=1
//strTestCompare.CompareTo("b")=-1
//String.Compare("abc", "a")=1
//String.Compare("abc", "ab")=1
//String.Compare("abc", "abc")=0
//String.Compare("abc", "b")=-1
Console.WriteLine(String.Compare("abc", "abc").ToString());
Console.WriteLine("*******************String.CompareTo()********End**********");
//String.Compare from MSDN
//unsafe
//{
// // Null terminated ASCII characters in an sbyte array
// String szAsciiUpper = null;
// sbyte[] sbArr1 = new sbyte[] { 0x41, 0x42, 0x43, 0x00 };
// // Instruct the Garbage Collector not to move the memory
// fixed (sbyte* pAsciiUpper = sbArr1)
// {
// szAsciiUpper = new String(pAsciiUpper);
// }
// String szAsciiLower = null;
// sbyte[] sbArr2 = { 0x61, 0x62, 0x63, 0x00 };
// // Instruct the Garbage Collector not to move the memory
// fixed (sbyte* pAsciiLower = sbArr2)
// {
// szAsciiLower = new String(pAsciiLower, 0, sbArr2.Length);
// }
// // Prints "ABC abc"
// Console.WriteLine(szAsciiUpper + " " + szAsciiLower);
// // Compare Strings - the result is true
// Console.WriteLine("The Strings are equal when capitalized ? " +
// (String.Compare(szAsciiUpper.ToUpper(), szAsciiLower.ToUpper()) == 0 ? "true" : "false"));
// // This is the effective equivalent of another Compare method, which ignores case
// Console.WriteLine("The Strings are equal when capitalized ? " +
// (String.Compare(szAsciiUpper, szAsciiLower, true) == 0 ? "true" : "false"));
//}