[b]Note to admin-ish type people: There are now duplicates of this post in GHG and the FU forum! If you update this post, update its duplicates also! 
[/b]For those that are still looking to purchase TA check out these links:
Tomb Raider II/Total Annihilation - Bundle PC $14.95
Total Annihilation: Kingdoms PC $8.95
Total Annihilation (Jewel Case) $9.99 at Amazon
Total Annihilation Gold at Amazon
Total Annihilation: Kingdoms $9.99 at Amazon
Total Annihilation: Kingdoms (Jewel Case) $9.99 at Amazon
Total Annihilation: Commander Pack $84.99!! at Amazon
Total Annihilation Kingdoms: The Iron Plague $35.00 at Amazon
Millennium Mega Hits $6.95 at Amazon (TA is in it) at Amazon
I will continue to look for retail option on Core Contingency.
Added 2005-02-05:
Total Annihilation at BigDaddySoftware for $10.98
Added 2005-10-23:
Total Annihilation, Core Contingency, & Battle Tactics at BigDaddySoftware for $34.97
[b]Added 2006-02-15:
Free CD-Software.com has OTA for free - plus shipping & handling
Amazon.co.uk - Commander Packs from £21.99 and up!
[url=http://www.billigespil.dk/shop/default.asp]Danish game vendor - has TA and TA: Kingdoms as part of a “War RTS Deluxe” pack for 278,00 DKK (