<font color=navy>My favorite times in order are
First two weekends in December - yes, there are some lines on the weekends, but not during the week, and Disneyland Resort is beautiful when it's decorated. You do have to watch for rain, though (even as infrequently we get rain).
May-Early June - beautiful weather, flowers in bloom - it's really nice. Thing to watch out for here are the grad nights, when they close the park early to us regular folks, and the private party they have now and then.
September-early October -- kids are back in school, and the weather is still pretty warm - don't have to worry about rain, either.
Of course, with all of these, this is the time that Disney refurbishes attractions, so you have to keep that in mind. If you want to go when most attractions and entertainment is running, then you need to go during tourist season.
December - March (& sometimes April) is our rainy season, with most of the rain falling in late Jan-Feb. This season, I think it's only rained once or twice, so we're really due.