does anyone know or anticipate that DC will start making omnibuses of pre-flashpoint comics? I ask because I'd like to read those books but I'd rather not spend all the money itd take to collect the issues.

Omnibuses usually collect a author's run. I don't see DC making Omnibuses for every title pre-52. It will be done for Johns GL since first volume was announced and at some point Morrison's Batman but not every title gets the Omnibus treatment.

I'm hoping for an Action Comics omnibus. I'd like to read a lot of Superman.

Well, an action comics omnibus is very vague, as I said omnibus collects a certain story or run usually, like Johns' run or The death of Superman omnibus. If DC publishes something in omnibus form it has to be critically acclaimed and popular enough to have a readership big enough to buy the omnibus. The omnibus treatment is very rare.
But if you are interested DC published an omnibus called Superman: the golden age which is pretty good.

@squalleon:

Thanks for the info.

Omnibuses are usually quite expensive themselves.

Here are the big story events in DC univers : http://www.dcplanet.fr/timeline/

@pperspectiveandreality: I cant wait for the paperback Geof Johns omnibuses.