to beat Irfanview click here
It's only weakness is that you can't do much in the way of selecting things... It's a rectangle or nothing!
WHen it comes to batch converting it can't be beaten... you can convert almost any aspect, name,size, image type etc.
A lot of folk will recommend Picassa, from Google. I didn't get on with it myself, but you shouldn't read anything negative into that!
Also, another one cropped up on this forum recently, and I tried it, but I can't remember it's name!... It was something like "Faststone"
(For what it's worth, I'm a fan of ACDSee as well , and use that for viewing, Irfanview for batch converting, and PaintShopPro for "proper" editing.)