Here is a list of all TMGC+C passwords we know of so far.
(I'll update this list as new ones are revealed.)
TamaDepa doughnut___80155 05372 (thank you tarokaja)
McDonalds seeds_____17140 03794 (thank you tarokaja)
Hapihapi seeds______84328 41937 (from Tamaeiga web site after entering correct password)
Letter seeds________93151 09844 (from Exile - yes it works on a regular TMGC+C)
Chocolate__________a14751a26428a(February; when connecting it's given to boys only)
Cookie_____________m13231m37549m(March; when connecting it's given to girls only)
Ohanami picnic set_a82643a70716a(April)
Baked sweet potato_o58748o72213o(November)
Normally you get a connection gift by connecting two TMGC+C during the specified month. Bandai is releasing passwords for these gifts (here) near the end of each month, so you can still get these items even if you don't have anyone to connect with.
Thank you to tarokaja for providing passwords for the missing monthly connection gifts.
Edited by binary, 22 March 2009 - 08:05 PM.