Microsoft is releasing theme packs for Windows 7 very frequently these days. But on its Personalization Gallery's download page, you can see only 3 wallpapers being displayed.
Rather than download a 5-10-20 MB themepack and then find out that you do not like most of the wallpapers, you can preview the wallpapers first before deciding to download the entire themepack.
To do so visit this link on Bing Search. Here you will be able to see all the Windows 7 themes released by Microsoft. These themes are collection of wallpapers, window colors, and sounds.
Click on any theme whose wallpapers you'd like to preview.
The wallpapers will be displayed. To zoom in on any wallpaper, click on it.
See if you like the wallpapers and then take a call if you'd like to download the theme.
You will get to see a host of information here, including the wallpapers, number of wallpapers included, Windows color, file size, etc. Apart from 'newest', you can browse by editor's picks & categories here!