No real reason to upgrade to the AM3+ boards just yet. Performance numbers for the new CPUs aren't out yet, and while I have faith in what AMD is promising, I still want to see what it can really do before I start recommending them.
That being said, you just pretty much have to pick a vendor and go. The vendors for Memory that I trust are G.Skill, Patriot, Corsair and Mushkin. Since you've got an AMD AM3 CPU there, you're capped to pretty much the DDR-1333 speed without overclocking the RAM, so a matched set of DDR3-1333 should be plenty.
As for motherboards, I like ASRock and Gigabyte (with Gigabyte being preferred). Here's a couple boards that I'd be comfortable recommending. I use newegg for most anything, but you're welcome to get the board from anywhere:
A little oldish, but still very viable today:
Newegg.com - ASRock 880GM-LE AM3 AMD 880G Micro ATX AMD Motherboard
I used to buy MSI until I had quality problems, but I keep seeing this board turn up in positive reviews, so it might be worth a shot as well:
Newegg.com - MSI 760GM-P33 AM3 AMD 760G Micro ATX AMD Motherboard
My board of choice, also a little old as far as the chipset revision goes, but still very viable
Newegg.com - GIGABYTE GA-MA78LMT-S2 AM3 AMD 760G Micro ATX AMD Motherboard
Also a tad old in the chipset department, but I'm just trying to keep costs down for you:
Newegg.com - ASUS M4A78LT-M AM3 AMD 760G HDMI Micro ATX AMD Motherboard
and for good measure, here's some RAM recommendations:
Newegg.com - Crucial Ballistix Tracer 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) Desktop Memory w/ Red LEDs Model BL2KIT25664TR1337
Newegg.com - G.SKILL NS 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600) Desktop Memory Model F3-10600CL9D-4GBNS
Let us know if you need anything else.