C#

//get info on current proc
Process proc = Process.GetCurrentProcess(); 
//get array of process w/ same name
Process[] procs = Process.GetProcessesByName(proc.ProcessName);

//get array of process w/ name we're looking for
Process[] procs = Process.GetProcessesByName("foo.exe");

proc.WaitForExit()

// Wait 10 seconds for foo.exe to exit
bool exited = proc.WaitForExit(10000);
if (exited)
{
    // The process exited, do whatever...
}
else
{
    // The process didn't exit...
}

using System.IO;
using System.Diagnostics;

class BS
{
	static void Main()
	{
		// Show all the currently running processes for fun...
		foreach (Process p in Process.GetProcesses())
		{
			System.Console.WriteLine("Found process:{0}", p.ProcessName);
		}

		Process ourProc;
		Process[] procs = Process.GetProcessesByName("calc");
		if (procs.Length == 0)
		{
			System.Console.WriteLine("An instance of calc.exe was not running, launching one...");
			ourProc = Process.Start("calc.exe");
		}
		else if (procs.Length == 1)
		{
			System.Console.WriteLine("Found an instance of calc.exe to monitor.");
			ourProc = procs[0];
		}
		else
		{
			// There were more than one calc.exe running...
			System.Console.WriteLine("Don't know which calc.exe to monitor...");
			return;
		}

		while (true)
		{
			ourProc.WaitForExit();
			ourProc = Process.Start("calc.exe");
		}
	}
}