Adrian,
The two photographers that I value most in terms of accurate advice are Thom Hogan and Moose Peterson. Tom has an
excellent essay on tripods that really rang home with me. Basically, it breaks down to spend now or spend later. I started out with less expensive tripods and heads (Manfrotto and others) then found that I wanted something that was lighter and more versatile. I eventually ended up with two keepers, both carbon fiber. One is a Really Right Stuff (RRS) and the other is a Gitzo. The RRS is my goto tripod for 95% of what I do.
Here's a
Youtube video from Moose on the RRS TVC 33, plus a
Youtube from Joe Johnson, the owner of RRS. I use the RRS TVC 34L, a tall tripod that can support up to 50 pounds, plus a smaller Gitzo. I recommend getting the best tripod you can afford, and the tallest, and with out a center column. With a tall tripod, you can position the camera so that you can shoot star scenes, or wildlife in trees, plus you will have enough tripod to work side hill locations. The reason I say no center column is to allow the tripod to lay flat for work that is low to the ground. RRS and Gitzo both make tripods where the center plate is removable so you can change it out with things like leveling plates, or a plate with a center column if you really want that
extra height. I prefer the RRS design over the Gitzo because it has three locking screws that hold that center plate in position. Gitzo just used (Not sure if that is still the case) a friction collet that held the center plate in position. Lots of expensive gear has hit the ground when being carried over the shoulder, and the center plate slipped out.
There are a number of other good tripods out there, but the above mentioned are my personal favorites.
You will need a good ballhead for your photography, and there are a number of them out there. Regardless of which one you choose, I strongly recommend that you get one that has a Swiss Arca style locking clamp. You can then use your camera with an Arca plate, and it will fit any of the Swiss Arca style ball heads. My preference is for RRS and Kirk ballheads, with Acratech following close behind. I use the RRS BH 55 with the screw in type clamp, they also make a locking lever style clamp. When you think about mounting plates that attach to your camera, consider a 'L' plate. That allows you to switch from landscape to portrait orientation without moving the ball head. If you think you're going to get into wildlife photography, you might want to look at a gimbal style head. There are several good ones, with Wimberley being the standard bearer.
So, I've just spent a lot of money for you. If you want to get good gear at a lower price, I suggest watching the local Craigslist ads in the photography section. It might take a while, but it does show up. You can also go for good quality aluminum (are you young and strong) tripods like the Manfrotos, and do just fine. They are just heavier, and usually not as versatile. I do recommend that you go to a Swiss Arca style ballhead though. Acratech is the most affordable.
I hope that helps.
Steve