If you're going to use it with a 5D2 or 7D (with newest firmware), you can get excellent results using a good preamp into the camera's PCM recorder, provided you also use a decent microphone and placement.
The Juiced Link preamp clips I've listened to (that were using good microphones) sound virtually identical to one of my high end preamps with a good microphone when recording with a 5D2.
The Juiced Link is the most practical solution and into a 5D2 will have a much lower noise floor than any portable under $1500.
If you are wanting something not specifically for the camera, I'd buy an EMU 1616m and use it with a laptop. More bulk but it will be dead quiet and no distortion. The cheaper ($300-$500) portables won't sound too terrible until you A/B them with something good.
So it comes down to how picky you are about sound, how much you want to spend, how much gear you want to lug around... To put it into camera terms, I'd say the cheap portables are like a 18-55 kit lens, the Juiced Link like a 17-55, the 1616m like a 24-70 II. LOL, and yes there is audio stuff that is like a 200mm F2 L in both performance and cost. :-)
