Heya,
Doh! Correct, AM2+, not AM3. That's ok though. It only effects the choice between DDR2 and DDR3 ram. The only issue with you having an AMD CPU and going nVidia for your GPU means you have to be very selective of your motherboard if you want to every SLI (obviously not crossfire since you have nVidia). That limits you to specific chipsets. If you every plan on using SLI, then you have to get an nVidia chipset based recent motherboard. If you don't plan on SLI, you can get any chipset and be fine. Personally, I wouldn't bother with SLI. But it's your board, so you decide.
Here's a good overclocking, gaming, etc, motherboard:
TA790GXE
It's $80. Ships free. Takes any CPU up to 140W that is AM3, AM2+, AM2. It's the 790GX chipset and the SB750 chipset. These are excellent for overclocking should you ever go that route. The board takes DDR2 memory (any flavor, so 800, 1066, whatever you have/want), and takes up to 4 sticks, up to 16GB. Two PCIe 2.0, two PCIe 1.0, and 2 PCI slots. Huge expandability for all kinds of devices (TV tuner, WiFi, etc). It has 6 SATA ports and is RAID 0/1/5/10 capable. It also is AHCI capable so you can hotswap drives with ease (very handy). It comes with an onboard HD3300 GPU. This doesn't matter since you have a GTX260 already. But the nice thing about it is that if you ever want to go multi-monitor or add more than two displays to your setup, you can do it without buying another card because your onboard can add two more display outputs (HDMI and DVI output). And this board happens to be one of the ones that will allow you to have your onboard GPU active as well as a primary PCIe GPU active, so you can use both and have 4 displays active from this. Very nice for multi-display setups.
Now here's the cool feature. It has two PCIe 2.0 slots. The primary one (master) is actually in the middle of the board, instead of the first one. This is super handy and thoughtful. Why? Because normally these big dualslot GPU coolers drop down and cover up your other more valuable PCIe 1.0 slots on the board and puts the fan directly on another card under neat it should you have one there. Instead, they position it towards the bottom of the PCIe slots, so that the only slots it's over are the normal PCI slots. Less wasted revenue when using a huge dualslot GPU. That frees up your other two PCIe 1.0 slots for use, and your other PCIe 2.0 slot is the top slot. I mention this because you said TV tuner later on, and you'll want a PCIe Tuner, and this way, it's not sitting right on top of your GTX260's fan.
And finally, I have this board. I overclock with it with a PhenomII x4 955 Black Edition and Mugen2 cooler. I use the onboard HD3300 with my 8800GT to display on 3 different displays (2 monitors and 1 HDTV). It's a great board and will serve you well if you don't plan on going SLI. If you plan on SLI later, by all means, let me know and we'll get a new board.
Very best,
🙂