DateTime Functions In ASP.Net With ToString():

Function	Result
DateTime.Now;	7/5/2011 11:38:38 PM
DateTime.Now.ToString();	7/5/2011 11:38:38 PM
DateTime.Now.ToShortTimeString()	11:38 PM
DateTime.Now.ToShortDateString()	7/5/2011
DateTime.Now.ToLongTimeString()	11:38:38 PM
DateTime.Now.ToLongDateString()	Tuesday, July 05, 2011
DateTime.Now.ToString("d")	7/5/2011
DateTime.Now.ToString("D")	Tuesday, July 05, 2011
DateTime.Now.ToString("f")	Tuesday, July 05, 2011 11:38 PM
DateTime.Now.ToString("F")	Tuesday, July 05, 2011 11:38:38 PM
DateTime.Now.ToString("g")	7/5/2011 11:38 PM
DateTime.Now.ToString("G")	7/5/2011 11:38:38 PM
DateTime.Now.ToString("m")	July 05
DateTime.Now.ToString("r")	Tue, 05 Jul 2011 23:38:38 GMT
DateTime.Now.ToString("s")	2011-07-05T23:38:38
DateTime.Now.ToString("t")	11:38 PM
DateTime.Now.ToString("T")	11:38:38 PM
DateTime.Now.ToString("u")	2011-07-05 23:38:38Z
DateTime.Now.ToString("U")	Wednesday, July 06, 2011 4:38:38 AM
DateTime.Now.ToString("y")	July, 2011
DateTime.Now.ToString("dddd, MMMM dd yyyy")	Tuesday, July 05 2011
DateTime.Now.ToString("ddd, MMM d "'"yy")	Tue, Jul 5 '11
DateTime.Now.ToString("dddd, MMMM dd")	Tuesday, July 05
DateTime.Now.ToString("M/yy")	7/11
DateTime.Now.ToString("dd-MM-yy")	05-07-11

Note :

Exception	Condition
ArgumentOutOfRangeException	The resulting DateTime is less than MinValue or greater than MaxValue.

If You want to know more about datetime constructors, Properties, Methods, Operators etc. 

, Than follow this link :

http://msdn.microsoft.com/en-us/library/system.datetime.aspx

Some Other examples:

string date = DateTime.Now.Date;
1. Show Date as " Friday 13 August 2003"

 date.DayOfWeek + " " + date.Day + " " + date.ToString("MMMM") + " " + date.Year.ToString()

2. Show date as "Friday 13 August 13:00:13"  //time in 24H format

 date.DayOfWeek + " " + date.Day + " " + date.ToString("MMMM") + " " + date.ToString("HH:mm:ss")

3. Show date in 12H format with AM/PM as: "Friday 13 August 01:00:13 PM"

date.DayOfWeek + " " + date.Day + " " + date.ToString("MMMM") + " " + date.ToString("hh:PM:mm:ss:tt")