Here's a complete list of 'record setting' address balances over time:
date block transaction balance address
----------- ------ ----------- --------------- ----------------------------------
Jan 03 2009 0 4a5e1e4b:0 50.00000000 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa
Jan 14 2009 496 a3b0e9e7:0 61.00000000 1BBz9Z15YpELQ4QP5sEKb1SwxkcmPb5TMs
Jan 15 2009 586 4d6edbeb:0 250.00000000 19QKDUJtx9n7Vaga6nX1bVHdsnT4Khfyi6
Jan 19 2009 1055 8897ea9c:0 500.00000000 15oUEZFKAC8E8BTLt1s1jx4fPxumwB3ecr
Jan 22 2009 1296 59bf8acb:0 875.00000000 12higDjoCCNXSA95xZMWUdPvXNmkAduhWv
[36 records omitted for 12higDjoCCNXSA95xZMWUdPvXNmkAduhWv]
Jan 15 2010 34887 ffcea1e6:0 72374.36000000 12higDjoCCNXSA95xZMWUdPvXNmkAduhWv
Oct 02 2010 83231 689f1772:0 110001.00000000 1LUPDXYf9XD9Ee1AqCuM3gZCA3ZMKgTcgw
Oct 02 2010 83240 0ee1f4e6:1 120001.00000000 1NJWs6g6hQsgxqtpRxXLhZJwHYhH2P2bvx
Oct 02 2010 83243 31b00090:0 122001.00000000 1NJWs6g6hQsgxqtpRxXLhZJwHYhH2P2bvx
Jan 27 2011 104770 8f821069:0 400000.00000000 1AYtnRppWM7tWQaVLpm7TvcHKrjKxgCRvX
Jun 12 2011 130281 a09ac44c:1 432109.87654321 1KLahQtqDNAXvrjNyfvgSBtAhwco5ZxLp4
Jul 18 2011 136856, e4762860:1 434242.43424242 1eHhgW6vquBYhwMPhQ668HPjxTtpvZGPC
[36 records omitted for 1eHhgW6vquBYhwMPhQ668HPjxTtpvZGPC]
Jul 18 2011 136870 b96a37e4:1 474320.43424242 1eHhgW6vquBYhwMPhQ668HPjxTtpvZGPC
Nov 16 2011 153509 29a3efd3:1 500000.00000000 1M8s2S5bgAzSSzVTeL7zruvMPLvzSkEAuv
And this shows for record setting transaction sizes:
date block transaction amount
----------- ------ ----------- ---------------
Jan 03 2009 0 4a5e1e4b 50.00000000
Jan 14 2009 496 a3b0e9e7 61.00000000
Jan 15 2009 586 4d6edbeb 250.00000000
Jan 19 2009 1055 8897ea9c 500.00000000
Jan 26 2009 1945 5559270f 1000.00000000
Feb 09 2009 3645 cec658ac 2200.00000000
Mar 16 2009 7677 e6f00fa6 2400.00000000
Apr 20 2009 11666 eebd343e 3500.00000000
Jul 20 2009 19863 123a3968 6049.53000000
Oct 16 2009 25095 4aa98b18 9700.00000000
Oct 22 2009 25618 1aae9d58 11950.00000000
Oct 24 2009 25788 5d793270 12250.00000000
Oct 27 2009 25969 3cd9410f 13000.00000000
Nov 04 2009 26402 6029e51c 15500.00000000
Nov 19 2009 27525 f2e5fdd3 21850.00000000
Nov 19 2009 27528 67fc73c7 22500.00000000
Mar 06 2010 44006 23709241 23247.39000000
Jul 12 2010 65566 ba62e528 35000.00000000
Jul 26 2010 70527 b9d69463 46753.13000000
Jul 28 2010 70870 73ac0fdc 50000.00000000
Nov 04 2010 89583 3bc57f90 50000.01000000
Nov 06 2010 90003 70dab592 55000.00000000
Nov 08 2010 90505 1ec28eee 96999.00000000
Jan 27 2011 104770 8f821069 400000.00000000
Jun 12 2011 130281 a09ac44c 432109.88745232
Jun 23 2011 132749 3a1b9e33 442000.00000000
Nov 16 2011 153509 29a3efd3 550000.00000000
So both the biggest balance and the biggest transaction are in block 153509.
The transaction is 10% bigger than necessary due to some sub-optimal coin selection code in the default client. It makes sure, when using a set of different coins to make up the transaction inputs, that the selected coins total at least one cent more than the transferred amount. This is an attempt to prevent sub-cent change which would trigger transaction fees. However, in some cases there is no need for any change at all. In this case the 'spare change' it allocated was a 50k BTC coin. I've since submitted a fix for this issue. This 500k coin and its subsequent movements caused the spike in global Bitcoin transaction volume referred to in this question.
Data is accurate as of February 9th 2012.