I haven't played WoW in a long time, but I still have these bookmarks.

http://www.wowhead.com/

http://thottbot.com/

http://www.wowinterface.com/find.php

http://files.wowace.com/

http://www.warcraftrealms.com/index.php

http://wowvault.ign.com/talentcalculator/?skillclassid=6

I'm quite serious when I say the answer is "me." PM me or we'll talk on Vent tonight. The obvious places for literal spell breakdowns have already been listed; I can speak in much more languid and tangible detail.

Allakhazam's a good site for general info. Wow-loot's got some nice info about gear and such, but I think it's more endgame focused.

http://wow.allakhazam.com/db/class.html?wclass=4&showinfo=1
http://www.wow-loot.com/

You do know Warhammer is coming in less then a month right ;)? Reserve it at gamestop and get in the beta!

I will suggest a couple of websites

www.wowwiki.com Dallinor already suggested will be a very useful guide to most of your needs, suggest you look under this site for rogue talent builds for leveling and later builds. A lot of stats are explained at what they will become and the equations as well.

www.curse-gaming.com for a lot of add ons for wow
I highly suggest quest helper (will look up more when I get home I got a bunch that were nice but just can't remember for rogues)
quest helper - will post points on your map where to go for quests or to kill and once quest is done will return you to the quest giver if you can't help will be really nice for new players ;)

www.wowdb.com easily one of the better wow search engines due to people don't know about it. can navigate through quests or search for gear etc.

www.thottbot.com pretty much the same as wowdb but i prefer wowdb a lot more

To know about what stats are better then what I can go into high detail. addon I dont' remember but you can look them up on curse-gaming and shouldn't be too hard to find an addon to show the pros and cons of changing gear cause I did use one but don't remember what it was called I quit wow months ago but i can look up once I get home.

I could give a small example like what u ask in OP all these numbers are close assumption I don't know the equation but this is a pretty good guess imo.

4 agil vs 6 ap (assuming lvl 20)
6ap only will increase AP and at a low level I think 6AP is like .3 increase to dps
4 agil = 4ap .2increase to dps, increase crit by .28%, increase dodge by by like .2%

So of course 4 agil will easily be more beneficial due to increase to crit and dodge. Of course these mechanics can be looked up on wowwiki

Oh yea to look up weapons at a specific level I would suggest wowdb like above. They have one of the best search engines for wow.

About duel wielding you want a slow main hand and a fast offhand usually but there can be arguments. But if you are asking specifically which weapon like swords, daggers, maces. It really doesn't matter when leveling. Though when I leveled as a rogue I leveled under the combat tree and never used daggers cause of the tree.

Sorry this is all that I can think off the top of my head for not playing in months and also at work where all wow sites are blocked. Though the 4 websites I have mentioned should almost be all the resources you should need till you get to 60-70 then I can give you a few more sites on mechanics of the game.

You're not gonna find as much information for low levels..

For extreme high level theoricrafting I would advice EJ forums...

http://elitistjerks.com/

You will find all the high end information you need there with spreadsheets and stuff...

Keep in mind that with Wotlk coming in a few months some mechanics are bound to change...

Probably going to be another AoC :P

So pass...

I'm going to go out on a limb here and just assume my computer, as awesome as it was 3 years ago, can't handle the game.  I know it can't handle Age of Conan.  Also, I don't know anyone that is planning on playing that game while a good 1/3 of my work all play on the same WoW server.

I might just have to do that tonight or whenever I get my next chance to play (it's usually every 2 or 3 days I get to play, enough time to get my little XP bar to fill up nicely).  Thanks ^^

So I just got WOTLK beta through my email and only played 20 mins but I think I am going to sell it for some cash, I thought hey wotlk beta might make me play wow again but I remembered the cons about play wow and just going to make a quick buck :D
Though gnome deathknight kicks some ass

Goto the WoW Class Forum for Rogues...that's usually where I get/link to all the best info. usually, when some1 has some good info, they will provide it. WoW rulez!!!