I used to always adjust with a known calibrated image. That way, the results are pretty much OK.
I can live with brightness problems, just not odd color casts.
If you don't want to spend on a spyder right away, you can always do some "eyeball calibration" using something like this
http://quickgamma.de/indexen.htmlI used it before and it was pretty decent.
On the site they have Quick Monitor Profile which extracts the screen's ICC profile. This is a good starting point as windows can push some out of gamut colors and not care the slightest if it doesn't have an ICC profile for your device.
Best of all, it's all F-R-E-E !