DreadArchon said:
I like feats, spells, items, base classes, maps, and monsters. Crunch is good.
PHB2 is fantastic in the feats and spells section. Really good, but there are... more useful books out there. I *like* the base classes too, but others do not.
1) Are MM III or IV any good for entire level spreads, or would the basic be better?
IMO, the basic is the best and you really should get it IF you want illustrations and ip-protected critters that aren't in the SRD (Slaad, Mind Flayers, Yuan'ti, Beholders). If getting monsters from the SRD is not that big of a deal, then, well you have to decide what you really want. I'd certainly want it, but it depends upon your priorities.
1)
Fiend Folio has a great spread of monsters, from the low CR's to the mid 20's. It's probably my favorite non-Core Monster book. Unfortunately, it's a hybrid 3.0/3.5 book so you'll have to convert the DR of a lot of critters.
2)
Monster Manual III has a nice range of CR's, from the fractional to about 20. It has some very creative monsters, but it is plagued with errors. Most won't bother you, but I thought I'd mention it.
3)
Monster Manual II is a really mediocre book, but it does have lots of high CR critters and while it doesn't have as many 'omg cool' monsters as FF or MMIII, it DOES have a few creatures that I use over and over again. Downsides: it's fully 3.0, you can run most on-the-fly but some will require some conversion, the high CR creatures really don't deserve their CR's, and it has some butt-stupid creatures in there.
4)
Monster Manual IV gets a bad rap, but it DOES have some worthwhile stuff. It has sample lairs for some creatures (maps included), more info on each creature, and sample advanced creatures from the MMI (gnolls, drow, orcs, ogres, lizardfolk). This can be good or bad depending upon your preferences. It has has some really cool monsters, but overall much less than the other books. Also, the sucky monsters tend to stand out more because of the overall low quantity.
The other creature focused books (Draconomicon, Libris Mortis, Lords of Madness, Fiendish Codex I & II) are all pretty good, but you have to be really interested in the creature-type to make it a worthwhile purchase.
Lords of Madness and
Fiendish Codex I: Hordes of the Abyss are my two favorites from the series, both because of new creatures and the flavor contained within.
2) Are there any other WotC books that are good for DM's?
A subscription to
Dungeon Magazine.

Not from WotC (nor is it a book!) but it kicks all sorts of ass!
3) I don't think I need a DMG I (am I wrong?), but is the DMG II any good?
I refer to it on a regular basis because some stuff is not in the SRD. It's also handy to have at the table.
DMGII is okay... the first chapter has some good advice and the sample town might be pretty useful, but overall... not sure about it.
Advanced Bestiary (by Green Ronin) is good with one caveat: it's all templates. Sure you can use the sample creatures but using the book will require much more work than using... say
Fiend Folio or MM3.5. The usefulness of this book will depend upon how much work you want to do.
The
Tome of Horrors series (I, II, and III, by Necromancer Games) all are chock-full of interesting critters. They have lots and lots of monsters, many of which are pretty cool.
Get a subscription to
Dungeon Magazine. Seriously, even if you don't use the adventures you at least have maps, sample statblocks, plots, and new monsters to spice up your games with.