If I had to guess, Maps and GMail. I've been trying to get rid of Google as well, and there aren't really any good alternatives to Maps and changing email addresses is a hassle.
Gmail is used as a dumping ground - its basically a backup for my @me/@ucloud accounts. I do find it harder to track down old emails, but way easier to send new and receive new ones - the use of symbols and random changes google makes to gmail are irritating. The other is (off all things) blogger. I have a huge collection of years of work related problems and solutions. This will be moved soon.
Maps I don't really miss at all - where I am Apples are just as good for my occasional needs.