Please do, I have 28 of Terry Practchett's books (still lacking quite a bit) you cannot go wrong with Discworld and if you really get into them you will have a better understanding of my avatar.
For SciFi. I'd have to go with the Icerigger Trilogy. About the only good series that I've liked of Alan Dean Foster's. Another good book is the Sphere by Michael Crichton.
Foundation isn't a trilogy. Hasn't been for a long time. The four canonical books are Foundation, Foundation and Empire, Second Foundation and Foundation's Edge. I read the prequel, Forward the Foundation, recently. Iirc there are two more, "Prelude to Foundation" and "Foundation and Earth".
a good book i recommend to anybody is mogworld by Ben yahtzee Crowshaw its really good and very funny
I found 'shadowmancer' by G.P. Taylor pretty good, despite the christian religious themes in it. its a bit fantasy set in the real world, and I happen to know the area its set in very well. They were making a movie adaption of it some years ago because I watched the filming while on holiday in the area, but I don't know what happened because it seems the movie never got completed. a couple of other good fantasy series to read are the edge chronicles by paul stewart and chris riddle, and the 'old kingdom' series by garth nix.
I read a great novel about a serial killer once but... it is in Dutch. If you can read Dutch, the books of "Aspe" are quite nice.