I'm making a budget build essentially from scratch.
I decided that the phenom 920 was a good enough processor for my needs, so I went on newegg, and looked for a motherboard/cpu combo, but there was none.
I say go with the 955. If you ever need to get a newer AM3 board, you will be able to still use your 955 till you get a newer CPU. The 940 is AM2+ only. You probably won't be using 955 by the time you finally move to AM3, but it doesn't hurt to be prepared .
Yeah really if you plan to run 2 graphics cards I would go with the 790FX chipset so you can run them in full X16 by X16 mode.Otherwise just use a 790GX motherboard if you're planning on using just one card (It will run one graphics card in 16 X mode).With using 2 graphics cards on a 790GX motherboard they will run in the slower X8 by X8 mode so that would be a waste.
So you will desire the same combo that I got if you want to Crossfire 2 ATI cards and have them both run at the full 16X setting.