Could you please advise me some easy algorithm for hashing user password by MD5, but with salt for increasing reliability.
Now I have this one:
In addition to the HMACSHA1 class mentioned above, if you just need a quick salted hash, then you're already 95% of the way there:
private static string GenerateHash(string value, string salt)
{
    byte[] data = System.Text.Encoding.ASCII.GetBytes(salt + value);
    data = System.Security.Cryptography.MD5.Create().ComputeHash(data);
    return Convert.ToBase64String(data);
}
The real trick is storing the salt in a secure location, such as your machine.config.