Best series (for me of course) are the Discworld books by the sorely missed Terry Pratchett. I am in the process of reading the last book he finished himself (a Shepherd's Crown) which is obviously the most personal book he ever wrote. There might be others yet to be finished by his daughter.
next to that:
- Brent Weeks - The way of Shadows
- Harry Potter
- Young Wizard books
- Percy Jackson books
- The first three Dune books
- Robin Hobb - Liveship Traders
- CS Lewis - Chronicles of Narnia
- Douglas Adams - Hitchhikers Guide
- Darren Shan - Demonata and other series
- Most books by Harry Harrison (stainless steel rat etc)
And of course the commercial and other (MS/Meulenhof) books. No idea who published them abroad, I'm from the Netherlands.
-edit- By the way, there are currently three books (free for download directly from his website!) about James Potter, the son of by C. Norman Lippert.
Here's his website, download links at the top:
http://www.jamespotterseries.com/muggle_index.html