To get the consistent 'duh-duh-duh-duh-duh-duh-duh' sound, where the kick and bass notes sound like one long pounding stream of bass, you ought to choose a kick that has similar timbre to your bassline and should also end at the same frequency (or harmonic of) your bassline.
How I approach kicks and bass (not to be taken as truth, just a way of doing it):
Let's say I make a kick in soundforge that's basically a pitched sine wave, a la the Infected Mushroom tutorial. At the beginning of the wave it has a lot of high freqeuncies to make the snap and then it sweeps down to low sub freq's. Doof.
Of course I'll want to limit the length of the kick to no more than a 16th note (for a KBBB style bassline) or my kick will overlap my bass and cause my low freq's to get out of hand. If I wanted a K BB style bassline I would do the same but for a 1/8 note. To figure out how long it should be, I calculate the time of a 16th note (60/bpm = time of quarter note in seconds). So for a 140bpm track, 1/16note = quarter note/4 = (60/140)/4 = 0.1071428s. So I need to make sure my kick ends, at a crossover point, at 0.1071428s or it will overlap the bass and cause unnecessary peaks in my low frequencies. Basically I just find the crossover point at or less than 0.1071428s. (the alternative to all of this is to use side-chaining, but that's another post)
Now, the fun part.
A kick is just a pitched sine wave, which means it contains a *lot* of frequencies (as it sweeps from high to low frequencies), so why can't our kick be *harmonious* with our bassline? If you look at a kick's waveform, you'll see that it pitches down to the low sub freq's - why not have it end on a note that complements the bassline? It's easy enough to do, just select the last half or quarter of the kick's wave, delete it, and replace it with a sine wave of the appropriate pitch.
If my bass is in the key of D, I'll look for the lowest D frequency above 32Hz which happens to be 36.71Hz. I generate a few hundred milliseconds of a pure sine wave at 36.71Hz in Soundforge, and then zoom it to the same zoom as my kick (so that I can visually compare them). Wherever my kick starts to look like it has the same frequency as the sine wave, I'll select the nearest crossover point and delete the rest of the kick's wave. Then I'll plop in the same (or slightly less to get a crossover point) of the sine wave. This way my kick 'doofs' from the high frequencies down to the low frequencies, but stops when it hits the fundamental frequency of my bassline. Of course I don't have to choose the same note, but could pick some nice interval like a third or fifth - anything that is harmonious.
I'll then give my bass a little boost around 73.4Hz (twice that which the kick ends on) and voila - the kick and bass will sound like a steady drone of D.
DOOFBADDADOOFBADDADOOFBADDA...
peace,
-fuzzikitten