Got a 2nd hand T91(non MT version) for US$229 on ebay recently, quite a steal! A similar one end up US$320 2 days later, so I consider myself very lucky!
After some tweaking (uninstall bloatware, get Tablet function working in XP, GMA 500 HW working and Win 7 UI makeover) it is running up nicely. I like the weight, really quiet operation (SSD rules!) compare to the previous ones I own, and the screen is not too small to read. Though performance is slow for others so this one is strictly for ebook and playing offline movies. (only 30% cpu usage on 720P mkv with GMA 500 hardware decoding). Playing anything over 480p in Youtube result in lag.
Toshiba M200: the first tablet I bought, used for drawing on the go. But lately having problem with pen pressure not working sometimes so I sold it (use bamboo on normal laptop instead). The screen is nice with 1400X1050 which is great for reading any ebook, but a bit heavy to hold and hard drive making clicks every now and then. Battery life only last <2hr. Bought for $195 2nd hand, performance is top notch with Pentium M 1.86ghz and FX5200 can play legacy game quite well.
SmartQ V7: I thought with 3 OS (CE, Android, Ubuntu) and ability to play 1080P coupled with large battery (6hr+ on SD video playback) and 7" screen should be great for portability. But after using it for few days I found I just can't get on to it as I thought I would, and 7" 800 X 480 is too small for some of my pdf (txt book and some mags) so I sold it after few days, paid $229 for it.
Samsung Q1UP: was seriously consider getting this (torn between this and T91), was selling for $330 on auction site (really great bargain!), I love the Core ULV1500 cpu as it is 2X faster than Atom Z520, even though they got same clockspeed, and 2GB is plenty enough. But the 7" is too small for me, though it got the same resolution as T91 the text will be a bit small to read. The 7hr+ battery life is really juicy.
Random 10" Win 7 Atom tablet: was considering this as well, cost $378 on auction site, 10" seems to be perfect compromise between portability and readability. Only downside is the 90 minutes battery life.. I mean WTF? The portability factor totally got let down by really tiny battery life.