If you have files on the SD card that are neither photos nor videos, then the iPad can't/won't load them. And you can't cheat either, by changing 'my file.doc' to 'my file.jpg'!!
But you can transfer files directly from a PC or Mac to the iPad over WiFi without the use of iTunes using a third-party app, such as GoodReader or PrintCentral. I'm not familiar with GoodReader, but PrintCentral can transfer individual files or complete folders from a PC to the iPad. You use a free app that sits on the PC that provides access to all your files and they are then loaded, over WiFi, to the iPad and sit within the directory structure of the PrintCentral app. If you have an app that can open a file then PrintCentral gives you that option when you select it. So, for example, if you transferred a .doc file and had (as I do) Apple Pages on your iPad (it's their MS Word application), then PrintCentral offers you the option of 'Open in Pages?'.
Of course, you can also use a cloud service, such as Apple's own MobileMe to transfer files but that's relatively slow and it's a two-stage process - upload from your PC to the MobileMe cloud disc iDisk and then download the file to the iPad. The plus, of course, is that you have the files 'available' of the cloud server and not taking up space on your iPad.
Tim
Scotland