Additional data storage

I work a lot with video and need the addtional space to store large video files. I run an HP Media Center 3.0Ghz with 250Gb (primary) and 150Gb internal hard drives. I have 300Gb and 120Gb WD externals for storage of video files after capture. When I am ready to edit and publish video I transfer the files to my 150 internal. I know externals are not the best for data storage, but I need the space!