As people have said, I think word of mouth is among the most effective of ways that people hear about these things... on busses particularly. I wonder how much ads inside busses cost...? Probably way too much, but the number of people who've asked me about the GP2x or GP32 a while back when on one is rather impressive.
To appeal to developers... well, if I recall correctly, one of the things about the GP32 that appealed to so many was that, essentially, it was the same as an ARM developers board but about a tenth of the price (arm in a box, ram, framebuffer). If the GP2x has somewhat of the same functionality, maybe it'd be a good idea to search out anywhere where ARM are advertising their own bits of kit and look at getting ads alongside theirs. After all, they much be reaching a certain demographic with their own ads for ADS and hardware, and it'd probably be largely the same one as would be nice to attract to the GP2x. That's one thought.
The other is based on an observation about adverts in this day and age. Walk along the street one day and see how many garishly coloured ads your eyes just pass over. If you can count them. Now try to do the same with simple black-text-on-A4 crudely printed header+text ads which people have stuck in windows. If the text is the right size, those are the ones which stand out, because we're so used these days to coloured crap. What you can do with that... no idea, but it might be of use in trying to get people to visit the requisite websites from seeing something about the place.
If we're after another gadget-prone group of people, it might be worth looking into enlisting people in second/third year uni to make sure they're present at Freshers' week events and get out some fliers along with all the clubs and whatnot. Only disadvantage is printing costs (about £99 for 10000 simple small flier ads) and that you've no guarantee people won't mistake the ad for a club night somewhere.
Then... I suppose if some of the other advertising is paying off, you could organise demonstration booths in shopping centres (pricey) or airports (even more pricey - but it'd stand out from Baileys and car booths, and be relevant for people who wanted something to do on the flight).
Right... those are my thoughts, I think. Maybe I'll think of some more in due course...