PIO is right, you can book two months in advance.
We have done all the character meals at DL and this is what I think:
LOVE the Plaza Inn. We saw such a great assortment of characters there and the interaction was great. We had everybody from Capt Hook and the Fairy Godmother to the characters from Pooh. Minnie was there, but no Mickey and no princesses if that's your thing.
Surfs Up at the Paradise Pier hotel was so, so much fun for our family. I deliberately booked a late time and at the end, we were one of only two families left. My boys had a good half hour of one on one (or three on four to be more precise!) time with Minnie, Daisy, Mickey and Pluto. It was so amazing to see my two year old dancing with them, doing the old "Hi five, down low - too slow!" thing and telling them his life story. He might not remember it, but I won't ever forget it. It was expensive and I wasn't a huge fan of the food (DH preferred it over the others though) but I'd do it again in a heartbeat.
Goofy's Kitchen we did for dinner one night and again we had a great time. We actually met up with another family and had a lovely big get together. Because we were kinda having a party, we weren't as focussed on the characters, but they did seem to be a little more rushed here. The food was actually quite good here, but I think this was the most expensive out of all the character meals.
We did Storytellers and Ariels a few years ago. DH adores Storytellers for the food. Characters are lesser known than the other meals, you get critters like Chip N Dale and Meeko. Lovely restaurant though. We had a great Ariel at our meal there. She was the most in character character I've ever seen and she was so much fun. The food there was so so and only having boys (who don't at all like princesses), I don't see us ever really going there again.
We also really like the Blue Bayou. DH proposed to me there once upon a time so it holds a special place for us. We've also been to the one at Tokyo which is pretty cool, but doesn't help you

If you go, ask if you can have a table by the water.
In DCA, Carthay Circle is wonderful. Very expensive, but a lovely fellow Anzac DISer gave us her free dining voucher for here otherwise we wouldn't have had a chance to experience it. The food was the best we tried at Disney. Unfortunately the ambience was ruined a little by overtired kids (ours!!! - who we were overly concerned about disturbing other diners), but it was still a lovely, lovely meal. I love all the photos on the walls and just the ambience of the place.