The year is but 8 days in and so far we have heard reports of tablet computers from the following companies.
Apple: http://www.wired.com/gadgetlab/2009/10/times-slate-slip/
Dell: http://www.sfgate.com/cgi-bin/blogs/techchron/detail?&entry_id=54786
Microsoft/HP: http://www.pcworld.com/article/186172/why_the_microsofthp_tablet_is_a_big_disappointment.html
Techcrunch: http://www.techcrunch.com/2009/06/03/crunchpad-the-launch-prototype/
Lenovo: http://www.engadget.com/2010/01/04/lenovo-ideapad-u1-hybrid-laptop-by-day-unhinged-tablet-by-nigh/
Sony: http://www.engadget.com/2010/01/06/sony-introduces-dash-internet-viewer-touchscreen-tablet/
Notion Ink: http://www.androidcentral.com/notion-inks-smartpad-now-adam