Oops, I wrote that response without seeing what you had written!
I'm glad you're open to Duesseldorf and Altbier -- I see that at least some people are ready to look past some bloodshed over 600 years ago.
As for Bierpost, I ordered Sam Adams Boston Lager from them... but that's because that's the beer I grew up with. And I'm from Boston. So of course it was most appropriate for me on July 4th as an expat thinking of home.
Their US selection isn't huge, it seems. And I think they have fewer American beers than they used to. Sam Adams Boston Lager is one of the decent beers you can find on tap all over the country. If you like stouts, you might like Left Hand Milk Stout. Anchor Steam and Anchor Porter are both quite good. I'm not a huge fan of Sierra Nevada.
Keep in mind, though, that while these are good beers, considering the great prices you have, I don't know if I'd necessarily shell out so much money these small 35cl bottles. Although the selection of foreign beers in Germany is pretty bad, both the selection and the price of domestic beers is excellent. So if you do order, I hope you don't expect something wildly better than what you can already get in Germany. And it might make sense to get beers that are a bit more different from what's available near you... like the Anchor Porter or Milk Stout.
Hope this helps!