The Archos 70 looks like one of the best WiFi only, low cost tablet. Charbax does a rather mumbly video review, but the features are very nice, as is the price:
http://www.youtube.com/watch?v=FK3ovYyh-34

- HDMI out
- USB host (or so Charbax claims)
- 7" @ 800x480
- Stock android 2.1
- No Google Market (may be a 'feature' for some here -- though it can be loaded on)
- Kick stand
- $275 US

If I were looking for a WiFi tablet and wanted no more than 800x480, this likely would be it.