Time Formatting in APEX

Letter	Date or Time Piece	Examples
G	Era	G = AD
y	Year	yy = 09, yyyy = 2009
M	Month	MM = 08, MMM = Aug, MMMMM = August
w	Week in year	w = 35
W	Week in month	W = 3
D	Day in year	D = 235
d	Day in month	dd = 27
F	Day of week in month	F = 2
E	Day in week	E = Thu, EEEEE = Thursday
a	AM/PM	a = AM or PM
H	Hour in day (0-23)	HH = 23
k	Hour in day (1-24)	kk = 24
K	Hour in am/pm (0-11)	KK=11
h	Hour in am/pm (1-12)	hh = 12
m	Minutes in hour	mm = 30
s	Second in minute	ss = 55
S	Millisecond in second	SSS = 888
z	Time zone	z = EDT, zzzzz = Eastern Daylight Time
Z	Time zone offset	Z = -0400

Example :
DateTime d = datetime.now();
dateTimeVal = d.format('MMMMM dd, yyyy hh:mm:ss a');
Output :
April 04, 2012 02:40:50 AM