some information regarding tripods for photography can be found here:
http://bythom.com/support.htm
the page discusses tripod weight vs stability, ballheads vs. pan/tilt heads, tripod material vs stability, and stability advice for taking photos (for longer exposures, etc.)
if you cannot afford cream-of-the-crop gitzo legs and really-right-stuff heads, you might try sirui/giottos/manfrotto legs and kirk/markins/arca-swiss/acratech heads ...
don't forget quick-release clamps and plates (aim for arca-swiss compatible) so you don't have to screw on/off your equipment all the time (disregard if you don't mind screwing)
generally, a ballhead will allow you to position your camera body in a portrait position with a drop notch or other method, but pushing the ball into the portrait position also pushes the weight of the camera off-center and reduces stability. a movable center column (like manfrotto) would put the weight of the camera even further out away from the center of stability.
for stability, try to keep your camera/lens center as close to the tripod center as possible (don't extend the column, etc.). L-brackets and quick release clamps (really right stuff or kirk brand) for your camera body will allow you to use a portrait position AND keep the weight centered over your tripod with smaller lenses. big lenses generally have tripod collars to allow for easy portrait/landscape orientations.
whatever works for you ...
p.s. if you have lighter gear (like a micro 4/3rds camera, small lenses, or point and shoot) then the manfrotto 190 series may work. frankly it's a shade too short for me even fully extended (full extension = less stability). considering trying at a store with your heaviest gear before you buy.
It's time to replace my ancient tripod, largely because it does not allow me to mount the camera in portrait format with any stability.
I'm taken with the Manfrotto 190XPROB as it's so easy to change the centre post from vertical to horizontal ... but are there others that are just as easy ?
And my old one only has a pan and tilt head. Is it worthwhile going for a bulkier ball head - what are the downsides/upsides ?