Srlec, here you go:
Download Retail Windows 7 ISO from Official Website | Windows7hacker
You can choose from the original Windows 7 install disk or the post SP1 install disk, whichever you prefer. If you intend to install SP1, you may as well download the one with SP1 already on it, it'll save you a lot of time on the SP install alone, which has most of the original updates already rolled into it.
EDIT: Be sure, if possible to use a download manager, such as "Down Them All" in Firefox (this is one example, there are others), as this is well over 2GB (32 bit) and 3GB (64 bit). Burn it slow for best results.
Hope this helps!
Cat