You cant really get "cheap" tickets for Disney / Universal. Some sites offer a discount, but it probably wont be much.
You are almost certainly better getting a 7 day or 14 day pass rather than paying at the gate. I think individual day tickets are like 80 dollars each.
Both Disney and Universal want you to go in THEIR parks and not the other companies parks, so they price their 7 day and 14 day tickets low to encourage you to buy these passes and stop you going into the other companies parks (they make a lot of money on food and drink when you are in the park)..
You dont say how long you are going for but I did see a deal for a 14 day Disney pass for the price of a 7 day pass (but only on sale till 31st March). To be used by the end of the year.
Generally Universal tickets are cheaper than Disney tickets as they are playing "catch up" with Disney (lets face it Disney are number 1 in Orlando).
However when we went we bought a 7 day Universal pass and only went into a couple of Disney parks. We found the Universal parks excellent and Sea World was my favorite, a wonderful park.