There are annual passes available that include admission to Islands of Adventure and Universal Studios for approximately $100 or $160.
The cheaper of the two, the Power Pass, has black out days when it cannot be used. Check for these dates and see if your planned travel dates are compatible with that passes black out days.
The Preferred Pass, at $170, has no such black out days and offers other perks over the Power Pass including free self-parking. Currently, there is a promotion running that gives 2 years' park access for the price of one. Browsing this forum will reveal a topic with a lot of information about this offer.
My family is planning to visit Universal for three days during our upcoming trip. I've purchased a Preferred Annual Pass for myself, taking advantage of the second year free deal. We'll be using the discounts that my annual pass will provide to buy the rest of the family's tickets and to get discounted meals and souvenirs. We're fairly confident that this pass will pay for itself over three days use. Anything more than that is just a steal, any way you shake it.
If you opt not to purchase an annual pass, Universal is also offering a promotion for a 2 day/2 park ticket that has a 3rd day's admission included for free. This ticket, by comparison, is $103.26 after taxes. Clearly, the Annual Pass is an attractive offer.