With a laptop, almost any external card will be an improvement. I, too, was recently looking for an external USB card when I happened to be in Staples and they had a Creative (SoundBlaster) MP3+ on clearance plus a rebate that brought the card down to around $20. While not the card I had in mind, for that price I couldn't leave it there. Besides having the usual lineouts (what I wanted a card for) its got line ins, mic in (which my Apple iBook does not have), optical in , optical out (no opticals on my iBook either) and even an amplified headphone jack.
Even this modest card made a difference such that I wouldn't want to do any laptop listening without it. Most noticeably, the high end was now more defined and extended with less sibilance and break up. The headphone is surprisingly decent (minimal noise at max volume) altough I do connect the card to an external amp which does outperform it.
For $20, if nothing else this card verifies the benefits of using an external USB card in a laptop. Despite the fact that the iBook card is reasonable for a laptop, cramming an internal card into a laptop has to result in added noise and heat adversely affecting the potential of any internal card.
The MP3+ was on clearance because it has been discontinued and replaced by the similar SoundBlaster MP3 Live. Creative confirmed for me that they are similar, althought the newer card has 24/96 khz sampling which doesn't factor unless using the card for recording purposes. I would recommend searching the internet as I am sure there are more of these cards on discount somewhere.
I do have my sight set on the M-Audio Transit. However, I am hearing that it presently has problems with the new Mac OSX 10.4 (Tiger) release. As a side note, I should mention that Creative does not sanction their cards for Mac use, but the MP3+ works just fine. Of course, the value added software included does not.
I can't speak from experience with the M-Audio card but my results with the Creative card led me to emphatically recommend that you do get an external card.
