For AWD at/under $30K, forget Audi, Volvo or other "upmarket" brands. Just ain't gonna happen.
The best value, by far and away is the "base" Impreza at less than $25K including most power options, AC and of course, Subaru's superb AWD system. The Matrix will get better mileage, but the AWD AT Matrix is not a fun car to drive. I found the AT versions with ratios completely mismatched to the engine and it just kinda droned along fighting the lack of low end torque. I bet the AT would be a much better match to the Camry's much more powerful four banger. Maybe Toyota just swapped in the same ratios?
Also, on the Subie, you get four wheel discs and ABS. You get side bags on the 06 models as well. Subaru upped the value equation on the 06's with a very small price increase and a few more features and bit more power.
As to the Forester, it's also revised for 06, and better than ever. You'll be "stuck" at a base model to keep things under $30K, but even the base is a pretty nice stationwagon. According to my insurance company, it's NOT an SUV, but a "stationwagon" and that saves us a decent amount on insurance. (We have an 01 Forester and really like it, super reliable, fun, and hauls a ton of stuff...)
I don't know much about the Nissan, but people seem to like it. I can't stand our local Nissan dealers, so I haven't ever shopped their products seriously. The X-Trail would be a serious value contended against both the Subaru Impreza and Forester.
The CR-V just doens't turn my crank. People love them, and they're well made, but I found the driving a little uninspiring and soft. I'm sure they're great, but just didn't suit me.