Price and Performance I'd say either the ASUS Transformer or the Acer Iconia. Both are pretty much the same spec wise and around $350. That is, if you're wanting an Android device. If you want iOS you only have 1 options; iPad2.
What I've seen is that if you spend less than $300 on a tablet, you get what you pay for, meaning they are usually pretty junky. I was under impressed with the Kindle Fire. Haven't tried the latest Nook yet but both of these devices are readers first, then some limited tablet device after. So again, you get what you pay for.