The modmic is waaay better than the zalman clip on mic(granted it costs a lot more, but 30 bucks isn't exactly a lot of money) so if you're on the fence for the modmic, just get it and wait. Desktop mics can be fine for some people, but they pick up more background noise than something close to your face like a headset mic or the modmic.
Here's a comparison of the zalman vs the modmic in case you were wondering(I don't have a desktop mic to complete the trio of normal candidates).
http://dl.dropbox.com/u/5977077/zalman%20mic%20vs%20modmic.wav