I love being in DL when it's raining! We've been a couple times in the winter/early spring where it was pouring at night, and even DH, who generally hates being cold, loved it and mentioned how much fun it was.
We used to do the dollar store ponchos but I think the official Disneyland ponchos are worth it. They're very heavy duty (have lasted us several years now) and I believe if they get torn DL will replace them for free?
Waterproof boots will make your day much more pleasant. Uggs has a lot of cute leather boots that don't look like the typical Uggs. I have the Kesey boots and they are super comfy. And a billed hat under the poncho as someone else mentioned previously.