In an earlier post, I linked to a couple of quotes from Gerald Bray and D. A. Carson supporting the biblical basis for the doctrine.
Shortly thereafter Steve Holmes linked to my brief piece, suggesting that my framing of the issue as an exegetical one was a good example---or bad example!---of evangelical biblicism. (The post was merely about method, not about the doctrine, as Steve believes in the eternal generation of the Son and thinks it is virtually essential to Trinitarianism.) Steve's knowledge of historical theology dwarfs mine, but I would disagree when he says "I am fairly sure that no-one in the fourth century thought they could read eternal generation off the pages of Scripture." I would suggest that the Cappadocians, for examine, did think it was a biblical position that could be demonstrated through texts (though of course that does not preclude the necessity of theological synthesis and application, and of finding the "sense" of the whole of Scripture).
Keith Johnson---author of a very good book applying Augustine's trinitarianism to questions of pluralism and world religions---has a post at the Gospel Coalition on the eternal generation of the Son that applies to this discussion. He writes, "Although one might assume that Augustine's commitment to eternal generation is merely rooted in a handful of dubious "proof texts," nothing could be further from the truth. This doctrine is rooted in a rigorous and comprehensive Trinitarian hermeneutic." You can read his whole post for a summary of how Augustine sought to demonstrate this doctrine from Scripture.
For those who want to investigate this issue further, Kevin Giles has a new book out on the theology and history of this doctrine: The Eternal Generation of the Son: Maintaining Orthodoxy in Trinitarian Theology (IVP, 2012). Giles has written several books on the Trinity, seeking to advance an egalitarian interpretation on manhood and womanhood and arguing that it is illegitimate to appeal to the roles within the Godhead as an example of submission and equality. He has tangled with Robert Letham on these issues, but on this they are united about the correctness of this doctrine and its importance for the church. For this reason, Letham penned the foreword.
Finally, for any interested in a wonderful overview of "Scripture, History, Theology, and Worship" regarding the Trinity, I cannot recommend too highly Letham's The Holy Trinity (P&R, 2004). It's an outstanding resource.