Benedict Jacka doesn't mention Harry by name in his Alex Verus books, but in the first book, in the first chapter when Alex is explaining that he's a wizard he does throw in a line about a wizard in Chicago who advertises in the phone directory. It's a clever and quite cheeky little reference. If you've read Dresden you know what it is, but if you haven't it won't really throw you, just a small line that will make you go 'Oh really?' Jim Butcher obviously took it in the spirit it was intended as he provided a cover quote/recommendation for the book.
George Martin is one for leaving veiled references to other authors and characters in his ASoIaF books, they can be pretty obscure, but they are there. I particularly liked the reference to House Jordayne which I think is from the mountainous region of Tor.
Terry Pratchett also does it a lot. Can't think of any specific examples of the top of my head, but they are there.
Of course Jasper Fforde does it all the time with his Thursday Next novels as a lot of those take place inside works of classic and not so classic literature.
