The only two that I know about are the Neuros and the Samsung Napster YP-910GS. All Neuri and that specific model of the Samsung can broadcast music over the FM band.
In terms of size, I'm not sure what you would classify as too big? I have a Neuros, and it feels 'right' to me. It doesn't feel awkward with the size that it is, nor its weight. I'm sure that the Samsung is much smaller. But, I would be skeptical of its build quality. That's because they don't make them anymore, and it's only available at places like ebay. In fact, there is one on bid for $100 and 1 day left right now. If that one looks good to you, snatch it up now.
But, I have to say, the Neuros has of those extras that you wanted that the Samsung model doesn't. Ogg support. I'm not sure how important that is to you, but it was very important to me. The transmitter on the Neuros goes the full length of the range for FM radios, but I don't know about the Samsung.
I just wanted to inform you that those two transmitted using FM. You should look into both of them a lot before purchasing, I suggest. But, I wouldn't suggest the Lyra. I've seen some scary/horrible things done to the display units at stores. Like the toggles being pressed in, or ripped off. Very dubious . . .
I've researched and searched but i cant find something with the following:
Under $300 (on eBay)
built-in FM transmitter
Relitively good/average battery life
Relitively good/average IDV3 tag capabilities.
and shows up as a removable hard drive on the computer.
Not too big.
The other good qualities i would LIKE to have but do not need are:
capable of OGG vorbis files
really nice GUI
The closest thing i found is the RCA Lyra RD2780....
Thanks for any help