Its all down to what you want to achieve Personally i would go for a high end board
so you can pull as much out of your Phenom II X4 940 Black Edition as you can.
The M4A78 doesn't seem shockingly full of features but like i said its down to what you want to achieve.
Phenom II X2 550
ATI HD 4850 512Mb
Western Digital 500GB Caviar Black Edition 32MB Cache
Then I decided to pay a bit more and get a Phenom II X3 720. Then later I saw a Phenom II X4 920 for a bit more money. Then I thought I may as well pay a bit more and get a Phenom II X4 940. The same thing happend with the graphics card - I kept seeing something better for a bit more money.
Now I'm spending way more than I originally planned so I decided to look at motherboards cheaper than the Gigabyte. I'm not looking to break any world records or anything. A 3.5Ghz to 3.6Ghz overclock would be nice.
When I research a board one of the best sources I know of for data is the manual. ASUS posts all motherboard manuals on their site and it doesn't take anything special to download it. Just go to the Support/Download section and fill in the blanks from there for a *.pdf file of the manual. If you have any questions at all about what you can and cannot change in BIOS that will answer most of your questions.
Personally I've found the mid-range ASUS boards to be somewhat lacking in the AM2+ and AM3 arenas with the exception of their new 790X chipset board, which costs about the same as a similar Gigabyte board. Mostly it's the power control on the boards I find lacking ...
For what ever it's worth, I'd recommend the M3A79T-Deluxe.
Granted it is not one of the cheaper boards, But I find it a VERY stable overclocker with more than enough bells and whistles in the bios.
Check my Sig, I'm running one with a 940BE.
whoops I a dummy just realized iI misread your m4a78 for a m3a78 , here's my luck anyways with one step lower board
I got the m3a 78 cm version and its ok but I kinda wish I would not have cheaped out. I got a cpu clock to 3.4 real easy and just haven't tried any more yet. I don't think I can get the memory voltage up high enough for my memory but its all stable so i'll jusy wait till I can afford the Gigabyte or asus m4a79 version.