Wait for what?
Canon just announced their new EOS 50D, successor to last year's really nice (but in some ways leapfrogged by the Rebel XSi) 40D. Nikon just announced their new D90, long-awaited successor to the D80.
They're not really competing in the same market segment.
The D90 is, feature- and price-wise, positioned against the EOS 40D. It's got some interesting gadgets (like an optional plug-in GPS for geotagging your photos as you shoot) and gimmicks (like HD movie recording capability) and market-standard "must-have" features (live view).
The EOS 50D is the step-up from the EOS 40D. It's got a new sensor that, while higher-density and higher-sensitivity (ISO 3200 "pushable" to 6400 and 12800), is less noisy than the already good 40D's sensor. It's also got a shiny fast new Digic 4 processor and a cool new control interface to go with it.
It will be interesting to see the full reviews and try each of them out when they hit the stores.