What Jihadjoe says, chipset determines the RAM type because Core2 didn't have an onboard memory controller.
I am happily using a cheap MSI board with a G41 Express chipset
, which I picked so that I could pass down DDR3 modules from other machines. I don't think there's a huge disadvantage to running with a DDR2 chipset and RAM, but DDR3 is definitely faster and easier to come by in large quantities.
I just hopped on the lowest price board with the basics I needed and all solid-state capacitors. Like me, I'm guessing you're not aiming for the cutting edge, you just want something simple that let's you Frankenstein some old parts back to life. Hunt the clearance sections and offers pages for anything S775 and check the features/specs are what you want. As long as you stick to solid-state caps, you are likely avoiding the lemons from corner-cutting brands like ECS and Biostar who will avoid putting more expensive components on their boards to chase the lowest price at any cost. Even some of the older Asrock boards can be a bit shonky, in my experience.
I'd like to give some feedback on Nvidia chipsets but I haven't used one since the nForce2 a good dozen years ago. If I had to make a sweeping (and probably incorrect) generalisation, I would probably say that the 775 Nvidia chipsets were inferior to the Intel ones, but did one thing that the Intel chips couldn't: SLI.
As for your socket confusion, S775 was intruduced for the Prescott Pentium 4's and was largely replaced by S1156 when the consumer round of Nehalem (Core i3/5/7) chips first started appearing - there were lots of chipsets for S775 but newer chipsets basically upped the FSB support from 1066 to 1333MHz, allowing the later Core2 (like Wolfdale and Yorkfield) to run with official support. DDR3 support was added as a bonus, but I don't think it was a requirement for the 1333MHz FSB processors. Certainly some of the oldest chipsets like the DDR2-based P965 were capable of 1333MHz support after a motherboard BIOS update, even if it was not 'official'.