There are a lot of tablets coming out, but I don't think the majority of them are well built as they rushed the production of them to be available at a similar time as the iPad.
Hope you don't mind me saying what they are, since this is an iPad forum. I have looked at them all, and picked the iPad over them all. These are from a magazine feature called iPad vs The world.
Fusion Garage JooJoo - Linux OS - £320
Archos 9 PCtablet - Windows 7 - £410
ExoPC Slate - Windows 7 - $600
Pegatron Slate - Windows 7 - $tba
MSI WIndPad 100 - Windows 7 - $500
Asus Eee Pad EP121 - Windows 7 - $tba
I doubt these are good, as these OS are not built specifically for touch. Plus. a tablet shouldn't be a laptop replacement IMO. I think Nokia and Intel are building a tablet OS, not sure though.
Android tablets are
Google Android Tablet
MSI WindPad 110
If it is inappropriate for me to post other tablets, just say and I'll delete.