EMSVC2 waives activation fees, but I believe it expires 4/15. I used this one.
WELCOME10, I believe, gives 50% off purchase charges until 5/31/2011.

The rest of the codes I have recorded have probably expired, but I suppose they might be worth trying if you have nothing else that works:

GEN372 might take $5.95 off (as of 2/22/2011)
EMOCTWEL waives gift card shipping fees (expired?)
EMNOVCM1 waives activiation fee (expired?)
SM10 "no purchase fees" (expired?)
AFLSHP $5.95 off shipping (expired 1/31/2011?)
EMFEBVMC free free (expired 2/?/2011?)

Citi credit cards are reported to reclassify AmEx gift card purchases as cash advances. I don't recall seeing recent reports in the past few months of anyone experimentally confirming that this policy remains in place, but I would be surprised if it has changed.