I admit it, I'm a carnivore and I appreciate a good brat. Not many places in Seattle specialize in these, or at least what I've found. (Hint: if you have a suggestion, please review.)
Diggity Dog is that quirky little place that sits close to Green Lake, near the old Honeybear Ham place. They serve up a variety of brats of different types, along with the standard dogs. Their side condiment bar is actually very good. (1) It's clean, and (2) they have a bunch of different mustards, mayos, hot sauce, etc. plus all the onions, cheese, kraut and other toppings so you can build your dog just so.
I haven't been in a while, but may be returning more often now that I know they have a play area in the back of the place. So, I could have another great brat while letting the kids occupy themselves.
I had the Bavarian, which was very good, though next time I'm looking for something a bit more spicey. The salmon sausage looks good as well, but who are you kidding? Get the real stuff if you can.