I rigge a character then export it as a OBJ file. But later on when I try to import this file to another scene, no pose mode is available and all the Riggs are gone. How do I save my rigged character so that I can animate it in another scene?
Create a new group by clicking on the mesh, then shift click on the rig, then press CTRL+g and group them together.
In a second blend file, use menu->Link. Then select the blend file you just saved, look in the groups folder, and select the group you created. Your model will appear at the cursor. But since it is a link you can not edit the model at all.
Now pres CTRL+ALT+P select the rig and it will appear.
This is called a proxy rig. (I think).
From this point on, you edit the model in one file, and you animate it in the second file. It is kind of like creating a spreadsheet in excel then linking it to a word document. Making changes in the excel document will be reflected in the word document. So making changes in the blend file that contains the model and the rig will be reflected in the blend file you want to animate in.
This is a tip I learned form watching the BlenderCookie Animation bundle training. Absolutely worth the $80.00 for the bundle.