Samsung have a dock for the Galaxy Tab which connects it to a pretty much full-size keyboard, and props the screen in a position where it's like a laptop's screen. There are also a number of Android devices that have a video or HDMI out capability to output their screen onto a TV, often needing a special converter cable.
Bluetooth is an option for connecting keyboards, KeyPro (AppBrain Link) (Official Website) andTeksoft Blueinput (AppBrain Link) (Official Website) load drivers onto your phone to let you use Bluetooth HID to connect up many Bluetooth keyboards (trial versions are free to test your device's compatibility, but it looks like if you want to carry on using it you'll have to pay to register to make it work fully). There are other options for loading Bluetooth HID (keyboard) drivers onto your phone if you root it.
Also, see these previous questions regarding connecting peripherals, such as keyboards and mice, to Android devices using Bluetooth.
From Android Honeycomb (Android 3.1) upwards certain devices, that have USB Host support built into their hardware, can attach and use normal USB keyboards and mice (with the appropriate USB host micro-USB to USB converter cable). I have occasionally plugged in used a keyboard this way on my Motorola Xoom.