Of course, a great starting place is Haggadot.com. They have a bunch of 'clips' that people have uploaded that you can include in your own version. I haven't been very succcessful at using their whole system, but I have found a few great pieces to include this year.
There are a few from "My Haggadah: I made it myself" which are more geared towards a slightly older child (say 5-7) than my under 3 crowd, but definitely good themed coloring sheets.
I started my personal Haggadah with the text from Jewish Boston's "The Wandering is Over" which they used to feature as a Word Document download. That gave me all of the hebrew text, and a really nice format/flow.
Add to that some questions I took out of a few of the Haggadahs I own, and I think I have something going. This year I also added a lot from Reform Judaism's Seder for young children. I liked the songs, and plan to download them all to my Kindle to have them ready for the service.
I also bought these CD's, so I could have mood music and some other background music playing.
These are the Haggadah's we own:
And yes, we own at least a few more. Not that I own enough of each one to have an entire seder, but I like to have a lot of resources for people to look through. Each one has unique perspectives to share...
My family Seder on Monday will feature this Haggadah:
Which I like, and has a lot of great tid-bits. Of course, the reality is that I'm also sort of over it. We've used it every year for a very long time, and I don't think it really adds anything additional to the discussion anymore. Of course, with my family there isn't much discussion. They are always so concerned with getting to the food that we don't do much chatting.
At least I've finally gotten them to the point where we do the back part of the seder. We'll see how that goes again this year.