Over the years I have seen a few people transport a dog on a bike. What options have you seen? Please include a photo in your answer if possible.
I just googled "Bike Dog trailer" and got tonnes of results. I have heard that trailers from "WIKE" are good. Here is a pic of their biggest dog trailer:
I have also seen a few DIY dog trailers.
I like this quite a bit. The dog is just tied in so they don't jump around but they still get a good view. Found at Bike Trailer Blog
There is also the option to mount the dog's crate onto the trailer. I have seen lots of pictures of these. Basically you just need to put some bolts through the flatbed of the trailer. This is a more professional example from Tony's Trailers:
I guess in theory you could also put a small dog in your front basket, but I would not do that. If the dog moves around that will make your bike unstable, also the dog may try to jump out causing a crash.
I've been using a K9 Sport Sack for my 25 pound dog. https://www.k9sportsack.com The dog and I ride a couple times a week. It took awhile for my back and shoulders to get used to the weight but it's no problem now.
We have a bike trailer for dogs and have used it once. The backpack is much less of a hassle. No need for extra bike attachments. No storage concerns. No difference in bike handling when I use it. Rough surfaces don't jostle the dog around because my legs and back absorb the bumps.
My dog actually gets upset if I ride without him. He ended up liking riding more than walks and more than going to the park.