We actually started a year ago with a little bit of pre-k. This wasn't necessary in my opinion, but I was excited about doing something organized with my little ones, and my oldest was enthusiastic about it as well. So, I started doing a Letter of the Week type of curriculum that I pieced together. The main resources I used for this was Animal Alphabet Friends flashcards by Abeka, with the CD of songs to teach letter sounds. This was actually a gift for the girls at Christmas, and they LOVED it. My oldest was four at the time, and learned all of her letter sounds super fast because of the songs. :) I'll definitely use those again! The flashcards are a little expensive in my opinion, and my oldest may have learned quickly with the CD alone, but they did enjoy the pictures with the songs.
I printed a ton of stuff from Confessions of a Homeschooler for free. She actually has a Letter of the Week curriculum all put together that you can purchase for $15, but she offers a lot of the printables for free.
We did several printables and tried to do a craft at the end of the week. My favorite was "E is for Elephant" hats, found here. It was hilarious!
We actually only made it to letter K before we dwindled off, because I was in my third trimester with baby #3. I considered picking it up again, but we never did. We went ahead and moved on to Kindergarten in the fall. I'll write about that in a separate post. :)