It depends on how "halloweeny" you want it to be. Do you want it to be cutesy Halloween, Creepy/Scary Halloween, or just Fall-ish? A good default is always the bales of hay and pumpkins and cornstalks for the front porch; the stalks can be tied up with raffia or fall ribbon. If you want to go more Halloween specific, Martha Stewart's website is usually a wealth of ideas for decorations and food. I helped my parents put theirs together a couple of years ago and we went so far as to make the invites little severed fingers (plaster cast) in a box-a black ribbon tied around the finger telling the guests "don't forget". It was an all out kind of thing and took a lot of prep work, but it turned out great. All the lightbulbs in the dining room were replaced with black lights or purple or green lightbulbs for the dinner portion of things as well.
Last year we had one of our own-it was a costume party, so just seeing people arrive was a huge part of the fun. We wanted to keep it more simple, so we just used the decor we already had out for fall and Halloween. We also had everyone just bring some type of appetizer/finger food or treat so it was more of a pot-luck sort of thing. For games, we had a few things planned, but we ended up playing Scene It (80's music addition which was a riot!), and then mostly just talking and hanging out, although it did end up turning into a dance party that lasted until 2am! Oh-we ended up with a limbo contest as well. lol It was entertaining to watch Mr Incredible, a pirate and a vampire doing the limbo! I can't wait to see how it turns out this year!
For us it seems that most of the time when we "plan" games, we end up not doing them because we spend more time just enjoying each others company. You could always go the traditional route and do things like bobbing for apples, one line at a time spooky stories, things like that. There is a website called partygameideas.com that usually is a decent resource for ideas.
Oh, and for a cake, http://www.coolest-birthday-cakes.com/halloween-cake-idea... has a bunch to browse through.