A little more information would help.
What is your budget, hundreds or thousands?
Do you want zoom or prime lenses?
What is your intended use for the images, print or electronic display?
Will you mainly shoot in bright daylight or mixed/low light?
Depending on your answers, the Canon L-series lenses are excellent, but pricey. Tamron makes lenses which are arguably comparable in sharpness, for considerably less money and they carry a 6-7 year warranty.
As for portrait, something in the 85 - 100mm range and as fast as you can afford (f2.8 or faster). For landscape, wide to medium focal length. Speed is not as big a factor unless your chasing sunsets or other low light conditions.
One last thing to consider, the 20D adds a 1.6 multiplication factor to any lens you use due to the size of the sensor, which is smaller than 35 mm industry statndard current lenses are based upon. That is with the exception of a few new Canon lenses designed specifically for the 20D and digi-rebel line.
Give us a little more info for a better answer.