There is a stack of iPad competition arriving.
Numerous Android based tablets, a few windows CE based ones, Nokia might even released a scaled up Maemo tablet.
I'm not sure i'm sold on the android tablets, if google release a dedicated tablet edition it might be better, but right now they are just throwing the phone version onto them - Its scalable sure, but it has a lot of elements orientated for smaller phone screens rather than 7-10" displays.
Windows CE being.. well, windows.
Maemo 5/6 could be interesting, my impressions of the N900 is the OS could scale well to a larger screen, just depends if it's used properly.
But anyway, Apple needs rivals, otherwise they'd sit on their butt thinking the iPad is the greatest thing in the world. It's not perfect, personally i'm undecided if i'll go for one or not, i might just wait and see.