I'm feeling more practical and less philosophical today, so I thought I'd take the time to write up a list of various website resources that I love and share them with you fine folks.
Crafter's Tome has long been one of my favorite resources for lists of all the different recipes for each profession, along with the mats required, where to get the recipe, drop rate, and lots of different filtering methods. Kaliope and I appear to share a love for crafting in WoW and in other games, and she has definitely put forth a lot of effort into designing and maintaining this site. The only problem I ever see is that she is meticulous about confirming the presence of patterns and recipes, so when new patterns arise from a patch or similar, it may be some time before she updates the list. However, if she gets a Beta key for Cataclysm like she did with WotLK, you can be sure to see the Beta patterns up (tagged separately of course) for your perusal.
FreeWithMats: The purpose of this website is to show you a list of all the people on your server who have a particular pattern or recipe available - assuming, of course, they have updated the site with their own information. Back in BC, this website was full of loads of people who had all the patterns - looking for a rare glove enchant that only dropped in AQ? This website was the place to check if anyone on your server had that pattern. Unfortunately, when Wrath came out, they redesigned the site - losing all the people who had previously been listed. In reality, this was probably a good thing, as many players had likely stopped playing since posting their info. The problem is that people don't know about this amazing resource, and so very few folks are listed (I'm the only one on my server) which greatly reduces the efficacy of the database. I use it anyway as a handy check list of what patterns/recipes I have, and which ones I still need.
There are two sites in particular that are popular amongst people who want to check out the quality of another's gear, gems, enchants, etc.
My preference is wow-heroes. I like this particular site because it has a very easy to read interface. A quick scan of the progression bar let's me know how my gear is for relevant content. It also shows me a person's off spec, and makes it easy to see their professions, their health and mana, their guild, and which spec is most likely their main spec. It's easy to scan over raid statistics and achievements, what type of gems people are using, if everything is enchanted with the best enchant for their class/spec, where they got their gear, the iLvl, etc. It also makes it easy to find upgrades. WoW-Heroes is a raid leader's dream - esecially if you lead a lot of PuGs. This goes way beyond gearscore.
Another reason I prefer wow-heroes is that it is NOT Level 80 specific. Currently, it only will provide information for characters level 70 or above, but the level 70-79 analysis is very handy for leveling through Northrend when you are looking for upgrades, figuring out which dungeons are within your grasp, etc.
Be Imba is another site that many favor over wow-heroes, but I seem to have a lot of technical difficulties with it and find it a lot less organized with a less informative interface. However, Be Imba will pick up if someone is not meeting their caps (i.e. hit cap) which wow-heroes does not point out.
Raider101 - This is a wiki intended to provide something akin to "cheatsheets" for those who are looking for the basics of raiding for their class. One of the problems with a wiki is that it is often outdated, and therefore there are plenty of classes and topics that need to be updated. I'm currently working on the Disc and the Holy pages, but I'm slow when it comes to all the linking needed. When I'm finished with the update for the wiki, I'll make sure everyone knows.
I've heard some debates from bloggers about Raider101, suggesting that it discourages people from coming to our blogs, and instead looking for an easy one stop shop for the info they need. Personally, I don't really have a problem with that - I think that the people who regularly read my blog will keep coming back to listen to me make fun of myself, and I also believe that generating knowledge in a simple and easy to use format is a benefit for everyone. In a short, easy to read wiki such as Raider101, you aren't going to be addressing anything I talk about in my notorious "philosophy of healing" type posts. You go to your favorite blogs for discussions and debates - but sometimes it's intimidating to even jump into the discussion when you don't know the basics. I'm a big fan of guides that cover the basics for newcomers, so they can get up to speed and join in on debates and discussions quickly.
WoW Gem Finder is the best tool for gem shopping. By using a series of filters, you can determine what gems you need to pick up at the AH - you can separate them by color or stat or quality, among other attributes. The only issue I currently have with this tool is that it needs a filter to separate WotLK gems from BC gems.
WoW Collect is my go-to resource when I'm achievement hunting, and trying to figure out what pets, mounts, or tabards I have or need to get for the next achievement. One of the things I love most about this site is the ability to create a very simple checklist of what you have. I like checklists. They're like mini-spreadsheets.
Alchemist's Apprentice Cheat Sheet. Remember the days before ToC dailies, when you were out in Zul'drak, grinding out your Argent Crusade rep? Well, in case you ever decide to torture yourself in similar fashion again, this was my favorite URL for weeks.
If you have any other suggestions for websites that are particularly useful for raiders, levelers, PvPers, achievement hunters, role players, etc, shoot me a link in a comment and I'll take a look at it and see if I think it might be particularly helpful for my readers.