Nitrox is good for live-aboards & other 'high # repetitive diving' environments like shore diving Bonaire (and staying down longer on some other dives), and you need the certification card to get Nitrox.
Deep Diver is useful unless you've got good mentoring & read up heavily on deep diving on ScubaBoard.com threads (which I recommend anyway), since early on you have no idea how narcosis-prone you are, and having an Instructor handy to walk you through those first deep dives is a good thing.
Navigation should be quite good - I hope to do this someday. It plays to my weaknesses, though. I think Navigation is a weakness of many divers (including me), and if you just to just do tropical warm-water high-viz 'follow the leader' guided dives in charter boats in the Caribbean, you may not need it. But it's a good skill to have.
Rescue Diver - just did this one. It's highly recommended on ScubaBoard.com for good reason. It teaches you to think through thinks & hopefully avert panic. It's as much about taking care of yourself as anybody else, and both are good things. You need to be certified in CPR and First Aid to take it, though.
Advanced Open Water - can be a nice introduction to some different types of diving, and you need this before you take Rescue Diver if memory serves.
What all types & locations of diving do you plan to do? For example, a course in dry suit diving would be pretty useless to me since I don't own or plan to use one, but for some types of diving, a dry suit is a must.
Richard.