According to Stackoverflow ERDAS ER VIewer is the best tool to view GeoTIFF files. But their websites requires registration to download, I fucking hate them. Here is the direct download link without the registration form crap:

http://downloada.erdas.com/software/2011/apollo-erviewer-v11.0-win-x86/apollo-erviewer-v11.0-win-x86.zip

ERDAS ER Viewer is a free, easy-to-use image viewer featuring interactive roaming and zooming with very large JPEG 2000 and ECW files. It can also read most other common file types. Installing ERDAS ER Viewer also lets you embed large geospatial images in your Microsoft Word documents.
File formats supported: JPEG 2000, ECW, Universal Data Format (UDF) images, ER Mapper images, TIFF and GeoTIFF images, SPOT View images, ESRI BIL (ARC/INFO and ArcView) images, Smart Data ER Mapper algorithms, National Imagery , ransmission Format (NITF), ERDAS Imagine (IMG), ArcInfo ASCII Grid (ASC), Portable Network Graphics (PNG), USGS SDTS (DEM)

BTW my wallpaper project is completely insane. Each GeoTIFF tile is about 500 to 1,000 megabytes, and there are 32 tiles. I am looking for a tool that can merge these huge files. And God bless industrial large format printers can handle these files :)