Ok, your contacts you can synch to google. You should do this.
Info on the sd card should be safe, but always best to make a copy to the pc if you can.
All "paid" apps, you will be able to re-download from the market. The market may or may not remember free apps. Depends on the market version, and if it synched to google. But really, they were free, so who cares (good time to clean house).
Games, well, you can run titanium backup, and "maybe" you can restore the game data after reinstalling the app. Suppose it's angry birds
SMS, hasta la vista, unless you use a backup app like "my phone explorer", which backs up contacts to outlook 2007. SMS and other things to it's native PC app. In fact, it saved my ass yesterday (dou to my wife phone getting an HTC sense update, and it decided to turn on synch, and delete my contacts not only on google, but my phone as well)
You should wind up with a device, just like you bought it. When you re-log in to google (same account), you should get all your contacts back. If you select it to synch data (maybe it will), it should automatically start downloading most of your apps (best to be on Wifi).