While reading this answer to another question about the development of the Siddur (here, look specifically at the question about "Modern Laws Vs. Shulcan Aruch"), I came upon this question. Here is the selection that spurred the question:
The Rambam in hilchot tefila (Chap. 1) gives a brief history of Tefila. The beginning of structured Tefila began with Anshei Knesset Hagedola, who formulated the Shmoneh Esreh (Berachot 23a) which is the focal point of the Tefila... The first written siddur was edited in the 9th century , by one of the Ge'onim, Cohen Tzedek. <
Now, the question is not about the Siddur part of the quote, but about the Shemoneh Esrei.
What were the "ancient" Pre-Talmudic prayers like?
Are there any great sources for this research?