I'm know I'm posting this a little early (around 9,900 bronies), mostly so it isn't buried during the party since I'm sure the mods already have some awesome celebration in store for us for the actual 10k.
I used some guesswork, some research, and some creative interpretation to come up with the various characters and hope I did everyone justice.
So, despite the (sizable) amount of time I spend on this I'm still reluctant to post it. I'm pleased with the work and all, but I had to be selective about who to include and that sucked. Obviously I can't draw ten thousand ponies, so I had to pick the "best" redditor bronies, and let me tell you from experience: this is impossible. IMPOSSIBLE. There are around fifty characters in this image and that's less than a third of the list I futilely narrowed it down to, a list that continued growing even as I worked on the image. You all need to stop being so awesome all the time, you're killing me!
While I can't pick favorite bronies, I can have a favorite subreddit. /r/MyLittlePony is hands-down the best, made up of the absolute nicest, most welcoming, witty, hilarious, and inspirational community on the whole wide web. You guys have brought a lot of joy into my life. This is my way of saying congratulations and thanks!
You're all my very best friends.