I've been thinking about this a little more. I think Jordanville (or something similar, like the HTM prayer book) might be more useful for someone new to Orthodoxy. One book that is truly useful, although not as portable, is the Liturgikon published by the Antiochian Archdiocese. If I were only going to get one book for all my liturgical needs, as it were, that would probably be it. It's also very reasonably priced, considering the amount of content.
I thought the liturgikon was primarily for clergy? Does it include prayers for laymen?
I expect anyone wanting to become more familiar with liturgy might find it useful. It has all the stuff you'd expect to find in a Horologion, plus the Liturgy of St. John, the Presanctified Gifts, some of the services for Holy Week, the Kneeling Vespers, etc. A lot of very, very useful content, plus the rubrics. (I always find it frustrating when a prayer book only has half or three-quarters of the services.) As I said, if I were going to buy one book for all my needs, that would probably be it. That's not to say other books wouldn't be very useful, or that the Liturgikon has everything. For example, it doesn't contain any of the Akathists or Canons we'd be used to in the prayer books from the Slavic tradition (I am not that familiar with the ones from the Greek tradition, apart from the huge HTM Horologion).
For anyone with the Internet, though, I have to say the vast majority of this content is available somewhere online. A number of Web sites have daily prayers posted, as well as the Troparia and Kontakia for the saints of feasts of the day. In a pinch, one could always make a prayer book of one's own!