I use my Archos A5IT with Aldiko - it is a perfect ebook reader for the following reasons:

Aldiko has some unique features such as allowing the screen to dim way below that of the Archos brightness app (and you can do it with a simple swipe down the left side of the screen).

Aldiko has a wide variety of font colors and backgrounds (for both day and night use)

By using Calibre, you can convert many ebook formats to Epub (Aldiko preferred format).

the A5IT has long battery life.

I am not an Aldiko or an A5IT employee - just a very satisfied A5 owner (Although I often disagree with the Archosfans forum folks [post as formerceo])