EDIT: Because of this thread's popularity I thought I'd add to the OP to make it more informative.

I'll start with just a list of what I know already and think are worth mentioning. I'll be sure to add more as I find them. If you know of one that isn't listed here then post about it. Even better, if you have made a texture pack you think is worth sharing then please post here or pm me and I'll add it to the list. Make sure to include a download link and either images or videos of the pack in action.

JohnSmith's Texture Pack:
Probably the most most popular one out there. Not the most highly detailed textures (compared to something like the Oblivion pack) but still really easy on the eyes. It's the one I always seem to use even when new updates make it buggy and installing it requires a patcher (which he links in the thread) for the compass and a few other things to work properly (note: a lot of the best packs often need the same patcher and it's not that big of a deal). I like one of the more recent changes to the sun and how wood and stone tools are changed into more appropriate shapes for those types of weapons (giant wooden club for example). Most decent texture packs have these things but I somehow like JohnSmith's versions more.

GERUDOKU Texture Pack:
I can't believe I haven't added this as it's currently in my list of top 3 favorites and I'm using it right now. A modification of Duku's RPG Texture Pack (which is out of date), GERUDOKU is an amazing blend of detail and simplicity that most texture packs try for. While I preffer the way most items and tools look in JohnSmith's pack I like pretty much everything else in this pack more. If you're not playing online then you might like the how some of the paintings are made to look like banners and tapestries to decorate castles. While not meant to be as realistic everything just looks better with it and it works perfectly to give the game an RPG sort of feel. In the link above is also a metroid prime helmet mod that I have to try.

Here's the texture pack in action as its creator explores what is probably one of the best maps ever:

Minecraft Realistic 32X32 Texture Pack seems pretty top quality:
Highly detailed and a little more soothing with the deep greens I think. This is probably one of my favorites But I'd like to make my own mixture of this and JohnSmith's some time.

The Painterly Texture Packs have some pretty awesome stuff:
The best feature of this site is that it allows you to easily customize your own texture pack from a variety of options. They also have some decent holiday options for Christmas and Halloween, my favorite being the skeleton animal mobs; it also includes a more regal looking version of both gold armor and weapons to spice up your castle; and best of all they have an overly happy creeper and ghast option for when you're feeling down.
Make sure to also check out their Skylands map, I haven't tried it but it looks like fun. I just wish they would make it less like an adventure game and more like a random map that happens to be in the sky.

Frenden's Texture Pack
 looks fun:
A very cartoony texture pack. I only just found it and might download it for my little brother who just got into minecraft and is a little spooked by the creepers and other mobs sneaking up on him.
Why? Because this pack includes the silly creeper.

Awww.... That thing's adorable. I want one.
My only problem is this pack takes away some of the more serious elements of the game by making it look more friendly, but that's not exactly a bad thing to some people I guess.

The Tronic Texture Pack:
This one is simple and cool but somehow more interesting for it. I believe this pack is named after Tron which would make sense. If the last pack was too cartoony then you might want this one instead. It's just... sleek...

To anyone working on a minecraft portal mod, try this one pack for your test videos.


The fallowing are the packs I originally listed in this post along with videos. I really don't know much about most of them and had only found them then by searching youtube. I might try one or two eventually but for now I'll let the videos work as a description.

Basic Hi Res texture pack:
DL Link: http://www.mediafire.com/?5z7w4jy0wl6xfip

HD Oblivion texture pack:

Pokemon Texture pack:

Cave Story texture pack:

DOKU RPG Texture pack:

Last of all, here's hoping someone finds a way of making this possible some day:

That's all I have for now, feel free to post any finds. I'll be sure to update this post whenever I can.

 For anyone who found these forums through google or some other external link relating to minecraft, you should know that this is an online community that isn't based in minecraft, but a very large number of regulars here do play it and we have and entire subforum for any and all things minecraft (http://www.freefrag.com/minecraft/), that, of course, includes a number of servers hosted privately by a few of our members that you can find in the minecraft server listthread. Most if not all the servers require whitelisting at the moment and are meant for active members of our community (though official community servers are in the works). So if you want to join them you would have to first join us. So please join us if you're cool and want a place to hang out and talk about minecraft, other games, or whatever. Peace.