Как сделать так, чтобы панель задач моего приложения мигала, как Messenger, когда приходит новое сообщение?

Для этого используется API FlashWindowEx Win32. Документация к нему находится по адресу: http://msdn.microsoft.com/en-us/library/ms679347(VS.85).aspx

HWND hHandle = FindWindow(NULL,"YourApplicationName");
FLASHWINFO pf;
pf.cbSize = sizeof(FLASHWINFO);
pf.hwnd = hHandle;
pf.dwFlags = FLASHW_TIMER|FLASHW_TRAY; // (or FLASHW_ALL to flash and if it is not minimized)
pf.uCount = 8;
pf.dwTimeout = 75;

FlashWindowEx(&pf);

Украдено у экспертов-обменников gtokas.

FlashWindowEx.

Я думаю, вы ищете SetForegroundWindow.

Из записи в блоге Раймонда Чена:

How do I flash my window caption and taskbar button manually?

How do I flash my window caption and taskbar button manually? Commenter Jonathan Scheepers wonders about those programs that flash their taskbar button indefinitely, overriding the default flash count set by SysteParametersInfo(SPI_SETFOREGROUNDFLASHCOUNT).

The FlashWindowEx function and its simpler precursor FlashWindow let a program flash its window caption and taskbar button manually. The window manager flashes the caption automatically (and Explorer follows the caption by flashing the taskbar button) if a program calls SetForegroundWindow when it doesn't have permission to take foreground, and it is that automatic flashing that the SPI_SETFOREGROUNDFLASHCOUNT setting controls.

For illustration purposes, I'll demonstrate flashing the caption manually. This is generally speaking not recommended, but since you asked, I'll show you how. And then promise you won't do it.

Start with the scratch program and make this simple change:

void
OnSize(HWND hwnd, UINT state, int cx, int cy)
{
  if (state == SIZE_MINIMIZED) {
    FLASHWINFO fwi = { sizeof(fwi), hwnd,
                       FLASHW_TIMERNOFG | FLASHW_ALL };
    FlashWindowEx(&fwi);
  }
}

Compile and run this program, then minimize it. When you do, its taskbar button flashes indefinitely until you click on it. The program responds to being minimzed by calling the FlashWindowEx function asking for everything possible (currently the caption and taskbar button) to be flashed until the window comes to the foreground.

Other members of the FLASHWINFO structure let you customize the flashing behavior further, such as controlling the flash frequency and the number of flashes. and if you really want to take control, you can use FLASHW_ALL and FLASHW_STOP to turn your caption and taskbar button on and off exactly the way you want it. (Who knows, maybe you want to send a message in Morse code.)

Published Monday, May 12, 2008 7:00 AM by oldnewthing Filed under: Code

FlashWindowEx - это то, что вам нужно. См. здесь для документации MSDN

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool FlashWindowEx(ref FLASHWINFO pwfi);

[StructLayout(LayoutKind.Sequential)]
public struct FLASHWINFO
{
    public UInt32 cbSize;
    public IntPtr hwnd;
    public UInt32 dwFlags;
    public UInt32 uCount;
    public UInt32 dwTimeout;
}

public const UInt32 FLASHW_ALL = 3; 

Вызов функции:

FLASHWINFO fInfo = new FLASHWINFO();

fInfo.cbSize = Convert.ToUInt32(Marshal.SizeOf(fInfo));
fInfo.hwnd = hWnd;
fInfo.dwFlags = FLASHW_ALL;
fInfo.uCount = UInt32.MaxValue;
fInfo.dwTimeout = 0;

FlashWindowEx(ref fInfo);

Это было бессовестно подключено от Pinvoke.net