I'm a big planner, no matter what the occasion. I already admitted to spending a year planning our vacation. I also spend most of the year planning for Christmas and birthdays as well. One of the ways that I've found easiest to do this is to have my husband and my son both keep a current Amazon wishlist. It's a lot harder to keep my husband on top of this, but my son loves it. He lists toys that he sees on TV, or movies that he would like to see. He also usually has a fairly extensive list of books. I check the lists fairly frequently (since my son is only five I help him make his anyway), and watch for sales on Amazon. That also reenforces the items on the list, so that if I see something on sale at another store, I can grab it when I have the chance.
I also keep my eye out on clearance toy sales in any stores I frequently go to. Between the January Target toy clearance sale, and the more recent (April I believe?) KMart toy clearance sale, I'm already almost done toy shopping for Christmas for my son, and I AM done toy shopping for my nieces. I've spent right at $125 on toys, and the retail value totals over $400. A lot of the stuff was actually stuff on my son's wishlist, too. It included things like Legos, Geo Trax, and Cars toys. I've also recently picked up the second and third Pirates of the Carribean movies on blu ray/dvd combo pack for under $14 each, and two of the High School Musical movies for under $10 each, all of which were on a Christmas wishlist, and found on sale at Amazon because they were on said lists.
For books, I order a lot from Scholastic book orders. My son isn't in school yet, but I have a sister that's a kindergarten teacher, so we've ordered them from her for several years now. I rarely pay more than $2 for a book through the book order, but can still almost always find some every month. Since they are delivered to my sister (over 1000 miles away), she keeps them all together, and then mails them all to me, or I pick them up when I'm there, once or twice a year. That makes it easy to keep them hidden from Elliott, for Christmas. Even with him starting kindergarten in the fall, I think I might continue to order some from my sister (but probably still some at his school, too), for that reason.