I really enjoyed Philip Pullman's His Dark Materials trilogy. (Northern Lights, the Subtle Knife, and The Amber Spyglass) a really good, different read. While intended for teenagers, the books did the rounds in my office, and we all went to see the play in London!
I would echo ping ping's choice and as for Terry Pratchett The Johnny Maxwell trilogy is very good . Also although not a Harry Potter clone Mortal Engines by Philip Reeve Is a Great read and the first of four in a series.
Sorry to come back to this subject after so long but I was thinking if you are an adult reader (Although I think 15 years up would enjoy it) You might like to try The Portable Door by Tom Holt. It is an extremely funny Comic fantasy novel and is the first of an excellent trilogy. :-D
Ian Ogilvy wrote books like the Potter Books but J. K. Rowling's success overtook them even though he wrote his first, I don't know anything else about them but as they are of the same ilk you might enjoy them.