HomeExchange.com is reliable.
For airfares, be sure to search the airlines that don't turn up on the regular sites like Kayak -- e.g. El Al, Air India, Icelandic, etc. You can also sign up with various sites to get notifications when airfares go below a certain price.
If you're going to buy something pricy anyway, put it on your miles credit card. You can also buy U.S. savings bonds via your miles credit card -- you're not even spending any money that way, you're saving it. You can get household utilities put on your credit card -- of course be sure you're paying off your card right away so as not to accrue any interest charges, which defeats the point.