What should be my next purchase?

From your choices:
dust collection - shop in the house? you probably need it. I relocated my shop from the basement to the garage because of dust issues. In the garage I have gotten away without any dust collection for years, just a shop vac to clean up afterwards. Do you have a shopvac? There have been many threads here about homemade cyclones for shopvacs recently (might be my next tool project)
planer - I put off purchasing a planer for years. Unless you are working raw wood or reclaiming wood (this is why I recently purchased one), this could be put off. If you want to reclaim wood, I have gotten some beautiful wood from pallets run through the planer.
upgraded table saw - eh, I don't see much need. I will be using a contractor saw forever probably. If you have a decent quality contractor saw, keep it.

How about improvements to the tools you have now? You mentioned a router; a router table increases what you can do and precision immensely. I need a bench for my miter saw in the worst way; I find myself jury-rigging the weirdest setups to cut longer pieces. And, of course, extensions and outfeed tables for the tablesaw, if you have room.

Just some thoughts - it is difficult to say without knowing what you want to accomplish.

As others have said it really depends on what type of projects you do and what type of wood you buy. If you buy a lot of rough hardwood, I would have to say a planer. If it doesn't save you that much to buy rough wood and you buy good S3S then I would say a jointer. My 1st major purchase after the table saw was a jointer becasue I did and still do a lot of wook with solid wood. You can't beat a jointer for the edge it makes when glueing up panels. You can get a glue joint edge from a table saw but the cut has to be perfect. It you are like me you run it throught the table saw then right over to the jointer, no messing around haveing to cut again. On the other hand you can joint on the router table if you are careful, so that may be an option. It is my belief that unless you buy a lot of rough wood a planer is not needed. Most will disagree but for me it only saves .10 a bd ft to buy rough. Then I have to get out my planer and go at it. I really hate planing so much wood it is time consuming and really serves no purpose. But if you can get a good discount $.50 a bd ft then it makes sense for a planer. As far as face jointing I very little of that because the stock I buy is good and the good hardwood will come out flat when through the planer. The only trouble I have is with softwood (poplar,cedar,pine,fir) flatening out when it goes through the planer and then springing back to the odd shape. The only time I have trouble with wood like that is if I but it from one of the BORG's. Most of the time the wood I get from the mill is flat and no need to fave face joint. So after my long explaination I would buy a jointer and then build a router table.