Since manga should be read on real paper and not on a computer screen, here are some applications you can use to make reading scanlations a lot easier and fun. The next best thing to paper.
Here's some forum threads on how people like you and me view their manga:
1. Animesuki manga forum
2. Animepaper manga forum
I used some of the apps mentioned above, and here's my review to some of them:
1. Acdsee
Pros: This is the best general veiwer for images, very fast to booth. It has the all important zip and rar support, so you don't need to unzip your manga, just click and read on.
Cons: It is too bulky, bloated, and not really designed to read comics. It's not free.
2. Infranview
Pros: This is the best and fastest freeware image viewing application that is just a notch or two inferior to Acdsee. Free.
Cons: Does not support zip or rar archives. Since it's like Acdsee, it's also not really made to view comics/manga, so it's as awkward as Acdsee.
3. CDisplay
Pros: This app is specially made for reading scanned comics. It has zip, rar, and ace support. It has auto resizing of images to fit the height or width of your screen. Free.
Cons: It has bare bones interface that turned me off. Just note that a lot of people likes the no interface look, so it's just a matter of taste.
4. PicWalker
Pros: Fast all-around image viewer in the vain of Infranview. It has also an auto-bookmark function that is useful if you are reading comics and have to stop to do something else. Zip, rar, and ace support completes the package. Free.
Cons: It has problems (it does not display the comic) with archives that has other contents aside from images, like the text files to identify the scanlators of a particular title.
5. ComicsViewer [note: the site is in Chinese (or Jap maybe?) so if your browser (like mine) does not support these characters you will see some gibberish. This is not a big problem just click here for the english version of the app]
Pros: For me, this is the best manga veiwer of all. It has zip and rar support. It has a cool resizing engine that does not compromise the quality of the images. It has auto-bookmarking functions as well as manual bookmarking. It simply has a lot of functions to make your comics reading a pleasure. Try it dammit! Free.
Cons: The manual and help files are in Chinese (or Jap?), but if you have half a brain you don't need any help working this one out.
And that ends my round-up. Just note that this is not an exhaustive list, if you use other viewers then please leave your comment below.