FHR/FBR/FCR Breakpoints: http://forums.d2jsp.org/topic.php?t=2450747
I dislike jsp, bunch of pridehounds on US East (worse than me, surprisingly) but this post is the end-all be all of these specific breakpoints. Most players here have this information memorized for the most part (at least for the classes they play) but it's never a bad thing to have a beautiful link such as this.
IAS Calculator: http://diablo3.ingame.de/diablo-2/ca...schwindigkeit/
The link may be in german, but the calculator is in english. This gives ALL possible IAS information, be it merc or your own character. However, the Strafe breakpoints are incorrect. Do keep this in mind.
Updated Strafe IAS Breakpoints: https://www.diabloii.net/forums/thre...points.183692/
This is for the correct Strafe breakpoints, if you so choose to use strafe (maybe useful vs summoners/druids but I feel multishot or a 1pt pierce GA would do more, maybe I'm crazy) What's that? You're having trouble deciding what WSM your bow has? Well look no further, welcome to~
Arreat Summit: http://classic.battle.net/diablo2exp/
Most of the time, you'll be in the "items" section, looking up uniques, sets, WSM of weapons, defense of armor, requirements, magic prefixes/suffixes and which can spawn on rare gear, even crafted item recipes! This place has it all. Not really, but a lot of information here, enough so that it's still a VERY useful link.
List of Item Mods: http://www.chrisclarke.co.uk/D2stuff...Mods_items.htm
Don't feel like going through EVERY SINGLE POSSIBLE item to find what belt gives FRW while on Arreat Summit? This is your place. It only lists Unique/Set/Runewords, so keep this in mind. Magic/Rare mods will not be here. Either way it's EXTREMELY useful.
Damage Calculator: http://www.d2region.com/images/guide...mage_calc.html
This will show you what your LCS doesn't. It'll show you your REAL damage, not what the game fails to read. For instance, Grief doesn't show properly on the LCS. But with this you can see how much damage it can REALLY get.
Damage Equation: http://bfed2.diablomods.ru/site/inde...page=gm_damage
If you don't trust calculators or really like math, does the same thing but you plug in the numbers yourself.
Attack Rating Calculator: http://d2region.com/images/guides/ka...s/ar_calc.html
Diablo 2 has a huge habit of lying on it's Character Screen. And it's entirely USELESS for PvP. This more is useful for GM Melee than anything, but it's a very HELPFUL link for anyone interested in how much of a chance they ACTUALLY have to hit. This also includes block chance to give you a real idea of how much you will actually hit.
Affix Calculator: http://diablo3.ingame.de/diablodb/af...=lod&patch=111
Acyroma showed this to me, I had no idea it existed. It shows UPDATED Magic Prefixes/Suffixes and Rare Prefixes and Suffixes based on the item type you are attempting to roll. Arreat Summit does have a few incorrect mods listed, so I'd suggest you use THIS instead. Do keep in mind, there are a LOT of affixes that just CANNOT roll here in D2PK. Once you know what all can roll, you can determine everything you'd need to know with this.
Diablo 2 Wiki: http://diablo.wikia.com/wiki/Diablo_II
This pretty much has every bit of information you would otherwise need. A lot of information on mechanics and how things interact. For instance: Did you know that Fanaticism gives EIAS not IAS? EIAS is any IAS given from a skill, such as Fanaticism and Burst of Speed. This is important when using the IAS Calculator, as putting your Fanat IAS under your IAS will change the entire calculation giving you a wrong breakpoint.
There is a LOT more information that may or may not be listed in these links (I personally have not scoured every single page to find it) but usually a google search will do. (Like for instance, All bow skills that give AR actually do NOT effect your attack rating despite showing on the LCS) And if you can't find it there, feel free to PM me and I should be able to help steer you in the right direction.