You need to decide what is most important to you.
An ultra portable will cost signifigantly more, than a similarly configured larger version.
If small is what you want take a look at the Sony T series or the Fujitsu P7000 there are smaller laptops, but any smaller is almost un-usable, at least for me. If you go smaller, the keyboards are too small to type with, and you have to squint at the screen.
The next size up is the 13-14" range, depending on brand you can get a laptop for about the same price of a 15.4" laptop. Sony's are still expensive, but they are one of the only laptops in that size range which has a discrete graphics option. If you don't care about that then go for one of the HP 14" laptops like the dv1000 or the Compaq dv2000z series. The HP/Compaq has a pretty good price/performance ratio. If you get a dv1000 series I would suggest a 400 MHz FSB and 1.6 MHz or 1.7 MHz processor, then overclock it to 2+ GHz.
If you are willing to go up to a 15.4" you will find many suitably priced laptops that fit your needs, except for small size.