In addition to the online platforms linked by the other commenters, it's also pretty straightforward to run Stable Diffusion locally, if your hardware is beefy enough: https://github.com/AUTOMATIC1111/stable-diffusion-webui

Various fine-tunes checkpoints for different content and art styles can be downloaded at civitai.

Stable Diffusion Web U by Automatic1111 is pretty excellent for doing image generation on your own hardware.

I develop the ai horde myself! It's the best and only one without a catch

Stable diffusion is free, you can install it on your computer

Bing works well up to a hundred images a week then just make a new account if you run out.

you can run SD yourself, super easy to do. Always a guide available on /g/.

Yes. Various, with various limitations.

The simplest is Stable Horde/AI horde. Volunteers donate GPU time to the public. Please do not abuse this trust by overusing it without giving back! Great for quick experiments, though, since it requires no sign-up. Also includes a "get probable description from uploaded image" function, I’ve just noticed:

https://aqualxx.github.io/stable-ui/about

Personally, I’ve been playing around with leonardo.ai. It has a payment structure, but the free tier is very generous, in my opinion. You get 150 free daily token. Images cost between 1-4 token. It has a prompt generator, and you can even train your own model for free. There are also a lot of community models, since every model is set to public by default. You can even browse public images and directly copy all settings/prompts into the generator or use them for image-to-image stuff.

The company is very much focussing on building an active community, which can be both good and bad. You are first put on a waiting list, but your account is automatically activated if you join the discord and write some comments. There are also constant community contests/challenges to earn more token.

https://leonardo.ai/

Edit: leonardo.ai techncally allows nsfw generations, but heavily discourages them. It has an automatic filter for any terms deemed nsfw. You may also not discuss how to circumvent that filter in the discord. (You may discuss how to bypass the filter to prompt safe for work images. E.g. you may discuss how to create Charles Dickens characters despite Dickens being filtered out.)

Here are few more, but I haven’t tried any of them:
https://stable-diffusion-art.com/free-ai-image-generator-sites/

I've recently used AI Image Generator. I've also bookmarked this to have a look later as that seemed to be a nice overview of options to selfhost.

You're looking for Openart.ai 😏

https://tinybots.net/artbot or just run stable diffusion youself, it is open source.

I've been playing around with Dreamerland for the last week or so. The app itself has almost no embedded ads which makes for a clean and usable interface, but it forces you to watch an ad every time you hit "generate" which can get tedious.

https://dbzer0.itch.io/lucid-creations

Is this kind of what you are looking for? It's made by the same person behind this instance

Out of the available image generators, Stable Diffusion is the best but be prepared to mess around with it to get the best results. If you have an iPhone or Mac, Draw Things is a great way to get started. If you want to dive head first into stable diffusion and have good hardware with lots of VRAM then try Automatic1111 as others have suggested.

Yes if you have a spare PC with a fairly recent nvidia GPU and decent internet speeds or a couple hours to spare for inital setup, you can selfhost InvokeAI. You can use stable diffusion with quite a few open models and its not complex to setup.

https://www.mage.space/

and

https://huggingface.co/spaces/runwayml/stable-diffusion-v1-5

don't even need registration, but don't expect too much of them.

Commenting cuz also curious

I have used https://neural.love/ai-art-generator

Don't have to make an account, but if you do it saves your generated images. Free use is limited to 25 steps, and 512x640 pixels. Paid use expands that.

If you want an easy to get into sd... check out easy diffusion. The beta allows for lara models now.

One thing I've always wanted to do is hack into OpenAI and leak the weights for GPT4 and DallE. Never got around to developing the skillset though (I've done a few CTFs, I'm super bad at them)