Any time i've tested a cheap clip on mic the output has been so low it's literally unusable. I have the speedlink one and also another attachable mic from that other place that sounds like sapling. Mobo has a half decent sound chip(Creative Sound Core3D) and the only mics i've found that work to any reasonable degree are the microphones on headsets and my old Logitech USB desktop mic (which i currently use - not had anything that compares to this yet).
I'm looking for a new microphone to (so i can avoid worrying about it breaking on the headset or having to factor that into headphone/set choice). What i've personally been looking at are the USB PC Condenser Microphones, some quite affordable options in the £10 - £30 range (check some reviews on that rain foresty place).
YMMV, some people get good results with lapel mics, for me they represent the worst quality mics(way too quiet) i've had the displeasure to use (and i really did have high hopes for the speedlink, shame really).