We present a catalogue of homogeneous measures of the linewidth parameter, v_e_.sin(i), for 373 O-type stars and early supergiants (including the separate components of 25 binary and triple systems), produced by cross-correlating high-resolution, short-wavelength IUE spectra against a `template' spectrum of {tau} Sco. We also tabulate terminal velocities. There are no O supergiants in our sample with v_e_.sin(i)<65km/s, and only one supergiant earlier than B5 has v_e_.sin(i)<50km/s, confirming that an important line broadening mechanism in addition to rotation must be present in these objects. A calibration of the area under the cross-correlation peak against spectral type is used to obtain estimates of continuum intensity ratios of the components in 28 spectroscopically binary or multiple systems. At least seven SB2 systems show evidence for the `Struve-Sahade effect', a systematic variation in relative line strength as a function of orbital phase. The stellar wind of the most rapid rotator in our sample, the O9III:n* star HD 191423 (v_e_.sin(i)<=436km/s), show it to have a `wind-compressed disc' similar to that of HD 93521; this star and other rapid rotators are good candidates for studies of non-radial pulsation.