All of these formats can be used as format strings with many dot.net framework functions (System.String.Format, StringBuilder.AppendFormat, etc...)

Base decimal value: 321543.23
Base Int32 value: 321545
Base DateTime value: 10/24/2014 7:03:21 PM

Note that some of these formats behave differently when grouped with other formats.
For example, notice the difference between {0:g} and {0: g gg}

Print formats

321543.23 - Currency: {0:c} $321,543.23
321543.23 - Currency with 4 decimals: {0:c4} $321,543.2300
321545 - Decimal: {0:d} 321545
321543.23 - Scientific: {0:e} 3.215432e+005
321543.23 - Fixed: {0:f3} 321543.230
321543.23 - General: {0:g} 321543.23
321543.23 - Number: {0:n} 321,543.23
321543.23 - Number with no decimals: {0:n0} 321,543
321543.23 - Number with 4 decimals: {0:n4} 321,543.2300
321543.23 - Percent: {0:p} 32,154,323.00 %
321543.23 - Percent with no decimals: {0:p0} 32,154,323 %
321543.23 - Percent with 4 decimals: {0:p4} 32,154,323.0000 %
321545 - Hex: {0:x} 4e809
321545 - HexFixed: {0:x8} 0004e809
10/24/2014 7:03:21 PM - Short date: {0:d} 10/24/2014
10/24/2014 7:03:21 PM - Long date: {0:D} Friday, October 24, 2014
10/24/2014 7:03:21 PM - Full (long date - short time): {0:f} Friday, October 24, 2014 7:03 PM
10/24/2014 7:03:21 PM - Full (long date - long time): {0:F} Friday, October 24, 2014 7:03:21 PM
10/24/2014 7:03:21 PM - General (short date - short time): {0:g} 10/24/2014 7:03 PM
10/24/2014 7:03:21 PM - General (short date - long time): {0:G} 10/24/2014 7:03:21 PM
10/24/2014 7:03:21 PM - Month Day: {0:m} October 24
10/24/2014 7:03:21 PM - RFC1123: {0:r} Fri, 24 Oct 2014 19:03:21 GMT
10/24/2014 7:03:21 PM - Sortable/ISO8601: {0:s} 2014-10-24T19:03:21
10/24/2014 7:03:21 PM - Short time: {0:t} 7:03 PM
10/24/2014 7:03:21 PM - Long time: {T} 7:03:21 PM
10/24/2014 7:03:21 PM - 's' but uses Universal time: {0:u} 2014-10-24 19:03:21Z
10/24/2014 7:03:21 PM - Universal sortable: {0:U} Friday, October 24, 2014 11:03:21 PM
10/24/2014 7:03:21 PM - Year Month: {0:y} October, 2014
10/24/2014 7:03:21 PM - All Days: {0:d dd ddd dddd} 24 24 Fri Friday
10/24/2014 7:03:21 PM - All Fractions: {0:f ff fff ffff fffff ffffff} 8 81 816 8162 81627 816273
10/24/2014 7:03:21 PM - All Eras: {0:g gg} A.D. A.D.
10/24/2014 7:03:21 PM - All Hours: {0:h hh H HH} 7 07 19 19
10/24/2014 7:03:21 PM - All Months: {0:M MM MMM MMMM} 10 10 Oct October
10/24/2014 7:03:21 PM - All Minutes: {0:m mm} 3 03
10/24/2014 7:03:21 PM - All Seconds: {0:s ss sss} 21 21 21
10/24/2014 7:03:21 PM - All AM/PM: {0:t tt ttt} P PM PM
10/24/2014 7:03:21 PM - All Years: {0:y yy yyy} 14 14 2014
10/24/2014 7:03:21 PM - All Timezones: {0:z zz zzz zzzz} -4 -04 -04:00 -04:00