Please, do me and all of your grown up friends a favor....Toss out the battery operated toys. They are not necessary. 1-2 per kid. Tops. I'm dead serious. Nothing is more annoying and brain stunting than a red monster doing the hokey pokey.
Instead.....check out toys that make "classic," toys, aka toys that help your child and are non annoying. I love Melissa and Doug toys, especially for this 2-4 year age. They are so sturdy and will last for years!
Also, Target carries the Parenting line of toys or a new favorite website ChildTrek (for all of you "go organic," moms.)
When you are looking for books for this age group, I am a big fan of Leveled Readers due to their short length (usually 20-30 pages,) and fun illustrations. They usually run 3-4 dollars a piece (cheap, cheap, CHEAP!) and can be found at almost any store, bookstore, or not. At a bookstore, however, they can usually be found on a spinning rack, and come in character books (think, Fancy Nancy, Spongebob, etc,) or plain stories. They also come in nonfiction ones, which is amazing.
One of the biggest prereading things to remember, is that it's not just reading skills they should be developing. Don't forget about the math! I, personally, loathe math, so if it happens to fall off the back of the truck of responsibilities, I won't feel bad at all. Unfortunately, my husband stinks at math also, so our child is in trouble already.
One of my favorite items to use are Math Counters. You can find them at any educational store, but some of my favorite come from Lakeshore Learning (here.)
When you are shopping for them, look for a set in plane old primary colors, with the details of the objects not painted different colors (it will be too confusing, trust me.) It is also best if you can have big and small of the same objects, (ie Big dog, little dog,) but make sure that the one objects comes in a variety of color (red dog, blue dog, green dog.)
So, once you have these (about 15-25 per can, but it's worth it,) start by having your child sort all of the items by color. . This is also a great way to work on small motor skills. Once they are done sorting by color, have them sort by shape, size (big/little,) put them into pairs, groups of four, or have them make a pattern with them. You can also pick up a pair of child tweezers (like for a science experiment,) or use a spoon, and have them use this instead of just their hands. Seriously, these things each almost everything they need to know before entering kindergarten (except shapes perhaps, since "dog," isn't really a standard figure.)
Puzzles, too, should be focused on and around at this prereading skills (because isn't learning to read just decoding a big puzzle? It's methodical, but it is a puzzle.)
Remember, this whole phase is all about the play time! Keep everything in a game like fashion, and you will be almost certain to keep their attention. Read, play, work, with an intention of sneaking in little snippets of lessons here and there.