Although I'll stick with the el-cheapo HobbyKing camera for the first few flights, in case I damage it learning, the image really isn't that great. I've been looking around on the FPV-LAB forum for a better camera that won't break the bank and came across this model:
600TVL SONY SUPER HAD CCD D-WDR Color Board Camera with OSD Menu DNR
Which for $50 seems damn good value, and others report that it works well. It has a 1/3'' SONY SUPER HAD II CCD and 600 TV lines, with an effective pixel size of PAL:753(H)*582(V). The specs seem to be the same as the Foxtech WDR 750 600tvl wide dynamic range mini cam which sells for $130 (in a case).
Here's a short video showing two different white balance settings. The quality looks pretty good to me.
@ Bruce, if you haven't considered this one for a review, it could be worth checking out. It seems this camera is available from a number of suppliers, some with a case being dearer.