Okay, here are the links. These will give the highest resolution. If you want a specific size to be cropped for you, replace =w9999h9999 with your own dimensions and and -n to the end. If you want a specific height or width and don't want it to be cropped, replace the dimension that you want but don't add -n to the end.
I'm using all of these in my app, SF Launcher as of version 0.2.5 (it will be live soon if it's not already). I tried many other cities, including Paris, Tokyo, Sydney, Las Vegas, Boston, Washington DC, and Los Angeles, and I got nothing.

San Francisco
Dawn: http://lh4.ggpht.com/IBBjIVcMzPNui1B...ER=w9999-h9999
Day: http://lh4.ggpht.com/eSJx22wFR4rSVcV...mg=w9999-h9999
Dusk: http://lh6.ggpht.com/G4Pl--INh2dHgjj...Sd=w9999-h9999
Night: http://lh5.ggpht.com/6rLbkZWhGVPxAVC...DA=w9999-h9999

London
Dawn: http://lh5.ggpht.com/_yM2g1jXS3Gxmov...wg=w9999-h9999
Day: http://lh6.ggpht.com/SdhQ1CORhZsvITV...vo=w9999-h9999
Dusk: http://lh6.ggpht.com/6OWsC7rvXQX8D4p...yQ=w9999-h9999
Night: http://lh3.ggpht.com/b95yYOipfo5Qmkn...B5=w9999-h9999

Default
Dawn: http://lh5.ggpht.com/LeDpxkfCDssG2jw...zA=w9999-h9999
Day: http://lh5.ggpht.com/bosDZkBJxNdwo-d...2w=w9999-h9999
Dusk: http://lh4.ggpht.com/DCGfFj7ILzkFXXD...4c=w9999-h9999
Night: http://lh6.ggpht.com/QgqUFGYoAxRkyvb...NI=w9999-h9999

Great Plains
Dawn: http://lh3.ggpht.com/-eRaUK3T0bbuJdh...gc=w9999-h9999
Day: http://lh4.ggpht.com/OBlnWOdeWdlVR0f...Kw=w9999-h9999
Dusk: http://lh5.ggpht.com/a7BiG1mNWojYk95...LI=w9999-h9999
Night: http://lh4.ggpht.com/BkE3y4c_8D3gTl2...1A=w9999-h9999

Seattle
Dawn: http://lh5.ggpht.com/x7wYMKpb2CGWK7G...ti=w9999-h9999
Day: http://lh4.ggpht.com/4kPg4fdvMJgnIgf...6w=w9999-h9999
Dusk: http://lh5.ggpht.com/_QetNT7lfWzeWXZ...s0=w9999-h9999
Night: http://lh3.ggpht.com/3ctptPGg5pMe2gj...yQ=w9999-h9999

New York
Dawn: http://lh6.ggpht.com/40TWudSUSlS-D-R...AI=w9999-h9999
Day: http://lh4.ggpht.com/OONnhdgrhh1x14g...Ww=w9999-h9999
Dusk: http://lh5.ggpht.com/qhVIITlUyAKh0l1...4Y=w9999-h9999
Night: http://lh6.ggpht.com/dq1rtn76Xertxh1...3z=w9999-h9999

Chicago
Dawn: http://lh4.ggpht.com/HkTiPVXRlpbfe8F...I8=w9999-h9999
Day: http://lh4.ggpht.com/XKhGtSHgY06OVIH...dg=w9999-h9999
Dusk: http://lh3.ggpht.com/Fc15BNNdT8-aBOR...2E=w9999-h9999
Night: http://lh6.ggpht.com/RlSDbCW2Fs5fHEz...cP=w9999-h9999

Beach (Honolulu, San Diego, Atlantic City)
Dawn: http://lh4.ggpht.com/IjAj-JLbrX9CtwO...1g=w9999-h9999
Day: http://lh5.ggpht.com/dhrhITD19-MNErP...pY=w9999-h9999
Dusk: http://lh6.ggpht.com/E8ubHH8XziIK5t3...-A=w9999-h9999
Night: http://lh4.ggpht.com/83jTpNKw0R4OW3h...tE=w9999-h9999

Tahoe (Probably other places too)
Dawn: http://lh6.ggpht.com/iM89ChxsvNmC7aj...q2=w9999-h9999
Day: http://lh5.ggpht.com/dhmfa5_k78ytD0v...pQ=w9999-h9999
Dusk: http://lh5.ggpht.com/dswhgQX4GaEif9s...oY=w9999-h9999
Night: http://lh4.ggpht.com/2oiPv-lr_VLFIHK...Uu=w9999-h9999

Berlin
Dawn: http://lh5.ggpht.com/8ubzNsDLQGQ8fYo...8t=w9999-h9999
Day: http://lh3.ggpht.com/q7AvSpLNCAOjlQA...kw=w9999-h9999
Dusk: http://lh6.ggpht.com/-30idiQtgOyr5KF...Yg=w9999-h9999
Night: http://lh4.ggpht.com/2JEs07oznuuvgcg...wQ=w9999-h9999

Austin
Dawn: http://lh4.ggpht.com/zAQwPdGWDc8a11n...KE=w9999-h9999
Day: http://lh4.ggpht.com/GB25hdlTR-h07vr...eQ=w9999-h9999
Dusk: http://lh5.ggpht.com/U7M2euecz7uMJg1...-T=w9999-h9999
Night: http://lh5.ggpht.com/weQrxcZZp-Ut00k...Ww=w9999-h9999