Did some Goggling on him... found the following to be of interest:
David Foote, Romano Guardini - The Essence of a Catholic Worldview
Silvano Zucal, The Intellectual Relationship between Joseph Ratzinger and Romano Guardini
Sandro Magister links to another essay by Silvano Zucal Benedict XVI Has a Father, Romano Guardini
Guardini's The Spirit of the Liturgy is available online - (no clue about the quality of the translation)
John Allen, Benedict's Final Theologian Quote
Apparently Jorge Bergoglio is a fan as well.