Check tire condition, looking especially for cupping (bad shock). Jack the front wheels up and check for loose ball joints, tie rod ends, etc. Just a visual check of the boots won't necessarily tell you if they are loose.
Control arm bushings can be bad too, but the usualy cause of such vibration is either a bad tire or a bad shock -- bent rim will also cause vibration, but it won't be intermittant...
Warped rotor and/or sticking caliper will do this too.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!