Got a particular budget in mind? That'll really help, otherwise everyone is probably just going to tell you to get the best possible parts lol. If you give a budget, those of us who have built computers before have an idea of where the $ should be prioritized and can make recommendations accordingly.
Personally I'd say the two most important features are a fast processor with several cores and hyperthreading along with lots of RAM (DDR3). I personally don't own an SSD and don't think it should be that high of a priority, but if you can afford it then go for it. I'm currently running an unlocked quad core Intel processor and 12 GB RAM, and my system flies. It takes a heck of a lot to bog it down. Sure, an SSD may save me 15-20 seconds booting up or a second or two when opening a program, but my processor and RAM doesn't leave a whole lot of room for improvement. I feel it's better to direct $$ towards a mobo that has SATA 3.0 and USB 3.0 capabilities. SSD technology is still in its nascent stage but has been getting a lot more attention and has become more affordable, and I think it's really about to take off. So I'd hold out and make sure your system will have the capacity to handle new developments in SSD tech by supporting SATA3. I'd wait a year or two for SSD prices to become more mainstream and for prices to drop, but if you wanted to follow Tim's recommendation and pick up a small SSD (32gb or so would do) to put your OS and stuff on, it wouldn't break the bank and you would probably see a speed increase.
I'm also not huge into video cards since I never game and don't do anything with video processing. I know you said you are interested in 3d software, and I do know that video cards help a lot with rendering, but I don't think it takes a super high end video card to deliver in that aspect. Get a decent one, but realize the high end ones are built mostly for gaming.