When the boys were younger, I used Preschool Express a lot! Once Henry (my sweet little bundle of joy) gets older, I'm sure I'll be back for more ideas.
Jean Warren runs this website full of toddler and preschool units/themes/everything! From art activities, to songs and poems, to free printables like the ABCs in 3 sizes (I describe how I used these in a post I wrote a couple years ago, Teaching the ABCs.), to cute snack ideas, and the list goes on and on!
She posts things under "Stations," and it can take a little getting used to where she 'filed' certain lesson ideas, but once you get used to the site, it starts to make more sense. She does tend to separate activities under each category by season. So if you're looking for Fall games, you'd look under the Games Station, and then find the Fall column. If you want Fall songs, you'd look under the Music and Rhyme Station, and find the Fall Column. Not quite as easy as having all the Fall activities listed in one location, but hey, it is a free site! So who's to complain!
You can also find things by unit though, in the Theme Station. For instance, since it's fall, you could find a theme of Pumpkins with activities such as Coffee Filter Pumpkins and Pumpkin Puppets. (Hey, I might have to add those to our fall plans. Even though my boys are Kindergarten and 2nd grade, a lot of these activities can be upgraded in difficulty so older kids can enjoy them too.) Then head over to the Music and Rhyme Station for some Pumpkin songs/rhymes like I'm A Little Pumpkin, and 5 Little Jack 'O Lanterns. And the Food Station has some cute Pumpkin face food fun ideas!
For parents/teachers of preschoolers - this site is an amazing resource! One that I have used time and again!