Lets see things they (any company) could sell that would get me to part with cash........
1. DDI version for 3.5 (and older as a wish) that allows for import of house rules. Weather this is inputed via XML or an actual wizard, if it's XML allow 3rd parties to create their own wizards for it.
Even better if WotC allows 3pp to create their own importable datasets.
Price point for this, honestly if they made regular updates, which I would easily buy the current DDI if it included this. As a stand alone product, $40-50 would be an easy buy for me.
I'm fine with Windows only, but I know many of my fellow geeks are going to want Mac compatible.
2. Spelljammer 3.5 update. Weather it's a license to Paizo for use in Pathfinder. Or even as a 4E release as a 90% fluff to 10% crunch.
Book could have chapters for the major systems & locations (Realmspace, Krynnspace, Greyspace, Rock of Bral, Voodini, Astromundi Cluster) and factions (Scro, Elves, Humans, Gnomes, etc). Most of it is fluff, really the only crunch needed would be the ship stats; how to build a ship; and ship combat section. This could have it's own edition independent combat system as well.
3. CRPG - I like computer games. I really loved ToEE even with the bugs. After it was patched using the official ones and the Circle of Eight it was a great game. Heck I played it again just this past weekend.
The 4E model does lend itself to well to CRPG's, we know it's possible to do it. Why not do it. Heck use the existing modules as the add-on modules for the game. Have a basic game there for $40-50, than use those modules as addition add-on packs at $15-20 each.
Heck even better if you get it consolable (XBOX/PS3/WII) where the players can downloaded it directly.
4. Currently WotC has a lot of IP in house. Is there a true harm in allowing a 3PP company to run with one you don't plan on re-releasing in the next year/two year cycle? I'm looking at Planescape; Spelljammer; Dragonlance mainly when I refer to this.
5. Print to scale mapping.
What's this you ask, basically the ability to legally buy/get the maps of various modules and print them to scale 1" = 5'. Even printed on plain paper have a numbering system that prints in the four corners where they match up. A DM could simply than lay them out as the group goes through or have it all taped together when they walk in.
Sure I can do this manually, and had a friend do this for me because he had a large graphics printer at his work. Scan in the map page, and print to desired scale for the mini's use.
It's something small you could provide easily.
6. Dragon / Dungeon Archive - would be nice to have. I already have mine handy like that so it wouldn't be so much a purchase for me as it would be a well liked one community wide.
So the first three are near instant buys for me, with the first being definite buy either as part of DDI or as a stand alone.