I have a GeForce 9800 GTX (512 MB) and it runs what I play very well (WOW, EVE, occasional FPS). Idling the card is about 45-50C, and under load (of the easy games I play) I get 60-65C and sometimes up to almost 70C.
My CPU has a cooler and it stays 29-35C. I have a HAF 932 case. I dont have a need to replace my card, Im just concerened that amount of heat may damage my Motherboard or other components.
My options are to replace the video card or maybe try a PCI slot cooler. Are these temperatures too high?
Your temps are okay. They're not the best, but then yours is a hot card so I wouldn't worry.
If you have the option to change your GPU's fan setting, I would take it off auto and put it to manual, 70% or something. See if that helps your temps. If you're able to add a side fan or a fan blowing ON your card that would help, but a slot cooler normally sucks are out of your case which wont really help your card stay cooler (as they'd be competing for air so-to-speak).
At them temps, your motherboard would be fine.
GPU's can normally go up to 90C-100C before failing, and some more than that, but even at that temps the heat wouldn't damage anything in your case other than the GPU itself.
The maximum temp for your card according to Nvidia is 105 degrees Celsius, your temperatures are well within normal range.
If your still concerned about your temps you can download Rivatuner here http://www.guru3d.com/index.php?page=rivatuner
this program will allow you to change your fan speed which from my experience are usually defaulted to a low speed. You can also use this program to overclock your GPU and change other settings, but you should only overclock and change other settings if you KNOW what you are doing. Otherwise just stick with changing your fan speed.