Okay let me tone this down a little bit. You want to use this for a gaming site right?
1) Will these games ever be made to run fullscreen or will they just be a certain size?
2) Are you just viewing the site through the tablet browser or will they be web apps?
If you really want a one size fits all, 800x480 is a very safe choice while still being big enough to visibly play the game on a PC. It also works for tablets, but then you have no fullscreen view of the games.
I would still recommend going for a resolution that works perfect for at least a 1024x768 resolution screen, in this case 1000x600 fits. Then for smaller screens you simply activate "Fullscreen in browser - On (Scale mode)" in the project properties view.
Your games will then fit anything smaller and go up till 1000x600 on a PC.
Hope this helps.
1000x600 is just what I like, but if you want to go for 800x500 then by all means do it!! It's still a very comfortable size to play games with.
Have a look at newgrounds.com it's a great example.