You can see more of Queen Puabi's headdress and jewelry at Sumerian Shakespeare. The site also has images and translations of Sumerian writings.
The International World History Project has an extensive section devoted to Sumeria. You can read a rundown of the gods and goddesses, a summary of Sumerian history and culture, and a section of the creation myth which gives a sampling of the divine soap opera the gods and goddesses had going on (a major influence on Urdaisunia!).
And, of course, we have to have ziggurats. The first and third pictures were particularly influential in how I envisioned the Royal Palace and the Temple of Ar at Zir.
A few more odds and ends: some ancient ships, and some Bronze Age swords. In Urdaisunia, these are the swords the Urdai used before the Conquest; the Sazars' swords are a new model and were inspired by Japanese katana.
Urdaisunia was only loosely inspired by Sumeria, so don't look to the novel for any kind of historical accuracy. But it was a fun world to play in, and I'll probably go back to it someday.
Finally, let me leave you with a musical tribute to the ancient world: