We just did exactly that! We've saved enough miles on American and USAir (which can be combined until they part company later this year) for 2 First/Business Class tickets to Hawaii. How did we do it?
1)We used our Citibank Advantage Visa wherever possible - but you must pay it off diligently each month to avoid interest charges. Plan on buying a big ticket item? Charge it to the card to earn the miles. For example, we used our tax refund money toward building a deck on our house. We charged the wood and supplies to the Citibank and then paid off the bill with the refund money. You can also earn miles just for opening an account. Check out the Citibank website.
2)We usually fly USAir, so we opened an account with them to earn miles and we also picked up their Visa card. We earned 2500 miles on our first use of the card. I used it to make a small purchase at Target, then paid it off and never used it again - except to purchase USAirways tickets and earn double miles.
3)I did some online shopping that allowed me to earn miles at Click Rewards. I needed the items anyway, such as books at Barnes and Noble. If you enter via the Click Rewards site, you can earn miles. I was able to earn about 2500 miles on doing very little shopping. Look for the promotions on the site. I got some great big miles from ordering magazine (that I normally read anyway) at Enews.com via Click Rewards.
4)Switch to MCI and earn miles not only on your calls (5 miles per $1) but also get yourself a bonus for joining. I used to be with AT&T when MCI called and offered miles to switch. They offered me 10,000 miles and I said, "That's really not very many miles." The saleman than said, "How about 15,000?" I said "Sure!" Don't be shy! Ask for more. They did spread the bonus miles out over 6 months to keep me, though.
So now after nearly 2 years, I have a little more than 100,000 miles between the two airline accounts. At this point, I can combine miles for tickets on either airline. I can do this until July or August of this year. At that time, if I don't know my travel dates yet, I can just order my reward certificate, which is good for one year. USAirways doesn't offer flights to Hawaii (as far as I know), so we will be flying on American which requires 100,000 miles for PlanAhead First/Business Class for 2. Of course, you can fly economy for only 35,000 each - but if you've got the miles, why not really make it worth your while!
Just out of curiosity, I checked the price of First/Business class tickets from Washington DC to Honolulu on American at different times of the year. The price came out to be nearly $10,000 for 2 people!

Wow! That's what I call getting your miles worth!!
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1995:
Disneyland Every Weekend!
Oct 1996: Port Orleans
Nov 1999: Wilderness Lodge
Aug 2000: Disneyland!
May 2001: Dolphin Concierge</font>