I've read all the Harry Potter books, not bad at all IMHO. Certainly better than a lot of the mainstream fiction that is churned out nowadays. I have picked up some fondly remembered classics from my youth for my children over the years, some aged well and others make you scratch your head and wonder how you could have enjoyed them back then.
Some that I have enjoyed re-reading are the Freddy the Pig books (by Walter Brooks, same guy who came up with Mr. Ed), the Brains Benton books, and some of the old Troy Nesbit books (Forest Fire Mystery etc). Some of the others, like the Hardy Boys and such, seem kind of boring now.
The Freddy books in particular are good for reading aloud to your kids when they are young, the animal characters are sometimes roaringly funny and Brooks' stories are engaging and well paced. Freddy is a far cry from Babe, he runs a bank, newspaper, detective agency, pilots a plane, rides a horse, writes horrible poetry etc. Lots of fun, and every book has some good educational stuff sprinkled in, from camping tips to money management to the importance of morals. Highly recommended.