The Windows Insider Program is now live, so the Windows 10 Technical Preview and it’s ISO. To download the Windows 10 ISO, you need to visit Windows Insider Program page and need to click ‘Join now’ button, which then asks to sign in to your Microsoft account, after sign in, visit this page (update: latest 10041 build ISOs page), scroll down a bit and note down the Product key and click on the download button for English 64-bit (x64) or English 32bit (x86).

Tips:

Download Windows 10 Technical Preview ISO 32-bit 

Download Windows 10 Technical Preview ISO 64-bit  

Read: How to burn Windows 10 Preview ISO to USB Drive?

Update October 6, 2014: Microsoft has released ‘Windows 10 Technical Preview Quick Guide’ in PDF format of 2.20 MB size containing 8 pages, you can download it from here.

UPDATE August 18, 2015: If you’ve reached this post to download ISOs for Windows 10 final, check the below links,

How to create or download Official Windows 10 ISO file by using Microsoft’s Media Creation Tool

Use this trick to get direct download links for Windows 10 ISO