I decided my next photographic investment would be a good tripod. I've been using an inexpensive Slik U8000 for years, and it's served me well. I was tired of trying to adjust the pan head quickly on location shoots, though.

Based on advice from this site [link] I purchased a carbon-fiber tripod and a ball head. I went with his less expensive solution:

Hakuba Carbon Fiber HG-503MX Tripod
Acratech Ultimate Ballhead with Detent Pin
Acratech quick-release plate for my camera
I also got the Acratech Leveling Base.

Initial opinions (after a few days and one shoot):

Acratech rocks. They have very friendly customer support (I had to check with them on the correct threading for the base). I ordered the head directly through the company [link] and used their web site to determine the correct quick-release plate. The head is light, easy to use, extremely smooth, beautifully designed, and locks tight. Apparently rubber knobs are now standard.

I recommend spending $10 for the Detent Pin - this is a safety feature to keep the camera from sliding out if you accidentally release the quick-release plate when the camera is not horizontal. Attaching the camera is slightly more difficult with the pin, though.

The Leveling Base is also well designed - see [link] for a review. In retrospect I don't know that it was necessary for me, although someday I may want to shoot panoramas.

What I found is necessary is a spirit level for the camera's hotshoe. I purchased the Manfrotto/Bogen 2 Axis Flash Hot Shoe Double Bubble Level, which works wonderfully. It's readable in low light, horizontal and vertical axes can be adjusted independently, and it can be flipped for taking vertical shots (in other words, it also works when the camera is on its side). At nearly $40 for a small plastic level, it's a little pricey, though.

The Acratech quick-release plate is the only downside to the head. It's well-machined, but it's specific to my camera's make and model - I can't loan the tripod to my Nikon friends unless they have compatible plates. It also attaches with an Allen wrench, so it's not quick to remove from the camera. While normally I'd leave it attached all the time, this means I can't easily use my Gorillapod or bean-bag pod. [Update - the plate is a standard Arca-Swiss type.]

The Hakuba tripod is decent. The center column can be shortened and the legs splayed out, bringing it quite low (about 11", not counting the head) for macro shots. It's light, and comes with a carrying bag and a center weight holder. The pan head that came with it seemed cheap, and the manual was entirely in Japanese. The twist-release legs take some getting used to, and have to be tightened fairly hard to lock. The feet do not offer spikes. In the standard position (there are two wider "splay" options) without the weight bag, it feels less stable than my old Slik (a very subjective observation). Fortunately the tripod wasn't the expensive part, and the ball head will fit many tripods.

I also bought an Op/Tech tripod strap (the two-loop one; the Hakuba doesn't have a center-column ring) and have found it useful. It feels considerably lighter than the bag that came with the tripod.

All in all, I'm pretty happy with my investment.

Caveat: I'm not an expert on ball heads - this is my first one.

Update (July 29, 2009) - The kind folks at hakubausa.com (via tocad.com) provided English documentation for the Hakuba tripod.

Update (August 5, 2009) - I purchased the Kirk Enterprises QRC-2 quick release clamp [link] based on advice from [link] . It works fine with the Gorillapod SLR-Zoom once I tightened the screw on the bottom of the Gorillapod. (The bean-bag Pod, on the other hand, is really designed to be tight against the bottom of a camera.) Note that there's no Detent Pin for non-Kirk plates, so you don't want to release the clamp when the camera is on its side.