aside from a bit of type-face correcting and a bit of errata, they're pretty much the same content-wise.
Personally, my suggestions are: PHB, DMG, Monstrous Manual (hardback), Tome of Magic, Players Option: Spells & Magic (for the rebalanced priest spheres and new specialists/specialty priests).
Yeah, they're about the same. I have the horse PHB and the black DMG, and that was never a problem. I agree on the books, add ToM to core because it's frequently referenced, and it just has a lot of great stuff. ToM is practically a 4th core book. Spells & Magic erratas the spheres and has a lot of cool specialist variants, plus it adds a number of spells for casters (some of which eventually ended up in 3e core) has some interesting rules like spell duels, spell points, and alternate spell casting systems, some solid guidelines for magic item creation, and has combined spell lists for the PHB, ToM and S&M. Probably the single best PO book.
There's a lot of 2e material out there, though much of it is campaign specific, so you can skip it if you like. Here's my recommendations on various optional resources you could eventually add to a normal 2e campaign though you can pick and choose from this stuff:
Arms and Equipment Guide: Used enough that's it's often considered core along with ToM.
Combat & Tactics: very good resource if you want to use minis, and makes a good alternative to Fighter's Handbook. Combat rules are to some degree a prototype of 3e, so if the combat rules are one of your big issues with the system, you probably won't want to use them. Has a big selection of weapons, including exotic stuff and firearms. Rules for siege weapons like catapults and cannons. Critical hits and crit tables.
High-level campaigns: Good advice for campaign building even if you don't go into upper levels. Also, additional powers for high-level characters, level-based saves, and true dweomers (10th-level spells).
Skills & Powers: YMMV. There's some stuff in this book that is broken. Some people love it. I'd say it's worth taking a look at this book though. Even if you don't want to use the full point-based system, you can still use CPs for the proficiency rules or as a 2e equivalent of action points. Also has some basic kits you can use if you don't want to dive into the world of 2e splats.
The Encyclopedia Magica and Spell Compendia are good resources, but not necessary. I'd say get them if you want access to a big variety of magic items and/or spells, but they shouldn't be the top priority.
World Builder's Guidebook is an excellent resource for campaign building, and is often considered on of the best 2e books. The advice is useful even outside 2e.
Notable splats:
Fighter's Handbook: It was the book to get for extra combat rules until Combat & Tactics. It's easier to use than Combat & Tactics, but less comprehensive. You can simply pick and choose between the two if you like.
Thief's Handbook: Adds a number of useful NWPs for rogue classes, and has some nice rules for creating thief's guilds.
Psionics Handbook: If you want to use psionics, you need the book. Otherwise optional. Also, if you want to use psionics, take a look at S&P which has revised psionics rules.
Bard's Handbook: Pretty much optional, but the bard kits add some interesting variants on the class.
Druid's Handbook: Includes variant druids for terrain types other than forests, plus some new spells.
Book of Humanoids: Rules for creating non-standard humanoid characters.
Monster Compendia: Most of your basic monsters are in the MM, and you could certainly get by with just that book. The MCs are for the most part campaign specific anyway, the first two that were for core 2e are all in the MM to begin with. For a normal 2e campaign, there are a few MCs that are somewhat useful for a typical campaign:
MC Annuals: 4 books with a variety of monsters compiled from multiple sources. The second book includes random encounter tables for the MM, and the third book has an index for the first 3 volumes. Good for when you want something unusual.
Planescape MC: The first one has most of your basic planar monsters like demons, devils, and angels. Good resource if you need those monsters. The other two aren't bad either, but not as useful overall for a general campaign.
Mystara MC: Lots of general monsters updated from Basic D&D material that can be used in just about any normal campaign. Another good source for unusual encounters.
