I've read the Canon book. I'm really puzzled why anyone would think it's a "bad" book. It's a collection of the most important essays in jurisprudence, so I suppose it'd be in order to criticize it for including what it ought not to include or excluding what it ought to include. But I think it gets the thing pretty much right. You may not buy some of jurisprudence, but it's hard to imagine someone being worse off for having read Calabresi & Melamed's classic HLR article, Holmes's Path of the Law, or (despite what some may think) Dworkin's Hard Cases.
On the subject of the thread, I didn't prep for law school (I read Law School Confidential, but not for any sort of "prepping"), and I'm sure it isn't necessary. That said, I don't think it could hurt, and to that end, here's some thoughtful advice:
Learning doctrine in advance is probably a mistake--since you might not learn it "correctly" in the sense of "consistent with a (/your) law professor's view"--but if you feel compelled to think about doctrine, I suppose Glannon is a fine thing to read.
It's really nice to have a basic familiarity with: 1) useful theories you'll apply in lots of (1L) courses, 2) the structure of the legal system, and 3) the supreme court. These are the sort of things that you'll pick up by osmosis throughout 1L, but you can learn them in advance to some degree. I'm not sure I can help too much with specifics (though others should feel free to supplement my examples within each type), but here goes.
1) Useful theories: It's hard to imagine making any sort of policy argument without some background in law and economics. If you have no familiarity with the area, you might google some basic background, but eventually you'll want to read Coase's The Problem of Social Cost and Calabresi and Melamed's Property Rules, Liability Rules, and Inalienability: One View of the Cathedral. Incidentally, both are in the Canon book others insulted. It's also nice to have non-economic theories at your disposal. Basic googleable familiarity with Kantian-derived theories might be nice, and you might consider skimming, e.g., Charles Fried's An Anatomy of Values (or Contract as Promise). You need not read the whole of either book. Other critical perspectives (feminist critiques, etc.) are nice but not my forte, and in any case, as important as they really are, your profs are not likely to emphasize them.
2) Structure of the legal system: There must be a book that's good here. I don't know it. In any case, really basic pages like the two that follow likely suffice:http://usinfo.state.gov/products/pubs/legalotln/http://www.quickmba.com/law/sys/
3) The Supreme Court: When you get into conlaw or criminal procedure (and even in other 1L courses), you'll talk about the justices of the supreme court. Professors tend to know a lot about the justice's personalities and their various approaches to jurisprudence, and they sometimes act as if you should too. A passing familiarity with the current court (at least) is good, and one way to get that is to look at modern popular books on the Court (Toobin's The Nine; Jan Crawford Greenburg's Supreme Conflict). You might also want to have heard of big cases and justices of the past, and this book seems promising:http://www.amazon.com/Peoples-History-Supreme-Court-ConstitutionRevised/dp/0143037382/ref=pd_bbs_sr_2/105-5848534-3482822?ie=UTF8&s=books&qid=1194411227&sr=1-2
Note that I haven't read it, so it might be terrible.
I think that's a reasonable start. If you do get the much-maligned Canon of Legal Thought book, I'd recommend reading Holmes, at least one legal realist (probably the Cohen piece), both the Coase and C&M pieces above, Dworkin, and a MacKinnon piece.