Gruppo - Dura Ace everything- except the chain and crankset... FSA K-Force Light for the cranks and a SRAM pc991 hollowpin chain (missing-link easy on/off is invaluable)

Headset - Standard, correct? One choice there- Chris King NoThreadSet

Spacers - Whatever... keep the carbon thing going, I guess

Seat - Veeery personal. Since you asked though- I like Specialized Toupes... Selle Italia SLK's are nice, although if I was in the market I'd probably try the SLC Kit Carbonio... or that SLR Kit Carbonio Flow...

Tires - I'm a Vredestein man. I think they make the best riding clinchers, hands down... can't beat that 145 psi. Go with what I ride... Fortezza TriComps for training, Fortezza SL's for race days if you're not on tubulars.

Tape - RavX Stitch tape. Or if you can't find that, it's better known as Stella Azzurra Eleganza (same company, same tape).

Stem - I know you didn't request opinions here, but that ea50 isn't in the same league with the rest of your setup. If you want to keep the all-Easton thing rolling, go higher-end there... or if you'll venture into other brands, then I can't say enough good things about the Ritchey WCS 4-Axis...