Any standard ATX motherboard will fit. The only problem you'll run into is the power button not working with some brands. (Asus for sure, I also ran into the problem with an MSI board)
See these two threads for more info viewtopic.php?f=4&t=5417viewtopic.php?f=3&t=2878
There is a fix for it, which is re-wire the black 5x2 pin header as mentioned in the thread linked above. Buy a NZXT Single Sleeve Front Panel Connections Cable Set and plug in the extender into the two pins next to the blank slot and your power button will now work. If you want your power button LED & HDD LED (activity light) to work then you have to wire 4 other slots (2 for each light) See the last post of the 2nd thread for more info.
To answer the second part of your question you would have to tell us more about your build to say whether or not you need to upgrade your PSU. If you don't plan on running SLI + OCing or anything like that then you'll probably be fine, I upgraded to a Corsair HX 650w modular unit just cause I wanted a cleaner look in my case. Plus it has stronger 12V rails than the Dell PSU. Btw if you do plan on switching your PSU you might have to unscrew the shelf below the PSU, move it up and then screw it back in, also there is some weird clamp/holder thing on the top of the case (above the shelf) that I had to remove (2 screws) to get my PSU to fit.