A fellow member here, wallcraft, often posts this ebook guide: http://wiki.mobileread.com/wiki/E-book_Reader_Matrix
I've had a look at it and it's a really good guide, would recommend you have a look and find one that meets all your requirements.
I personally just bought an Astak Pocket Pro and love it. Reads what I've thrown at it well except for lit files. But it doesn't have wi-fi. However it fits all your other requirements. You can see it here: http://www.astak.com/product.asp?serial=05EZWHT
It also comes with a number of colour choices and currently they are offering a holiday gift basket.