Depend on what you want. You can't expect miracles in a tiny palm sized package.
The reason the Fostex is called portable is because it's battery powered and able to be taken out into the field. That doesn't necessarily mean it's tiny enough to strap onto a monopod leg and be transportable...say for on the spot repositioning during a sporting event.
If you're looking for something that's gonna say fit in the palm of your hand, what you're gonna get is basically a bitbucket, but you'll still need mic preamps, mics, cables, etc. You hit on your options there...R-09, a new Marantz PMD-620 I think is the model number, Microtrack, etc.
If you want an all-in-one recorder where you need no external preamps or any other hardware, then the Marantz PMD-660 has a smaller footprint than the Fostex, but it's 16bit only. The Fostex is a little bigger, but it records in 24bit and has a ton of features that the 660 doesn't have. I can't comment on the Tascam because I've never owned it and don't know the unit much.
I don't know what exactly you're after...it sounds like you want something small enough to be able to kinda attach it all onto your tripod. However, if you want to run external sound into your camera, it might be tough to rig something up that just pops on and off your tripod real easy. You'll still have to deal with cables, tape, wraps, recorders, CF media, etc. no matter how you slice it....extra bags, etc.
I guess what I'm saying is that there is some setup regardless, so the advantage of the Fostex or the 660 being an all-in-one box usually is what people like in that it helps to eliminiate extra gear. All you need is the box, mics and cables.
Maybe you can rig something up and hang it off your belt or put it in something that hangs over your shoulder. Just take enough cable that there's plenty of slack so there's no tugging on the connectors.