Conference registration: The department usually reimburses conference registrations. Make sure to register early enough to get discounted prices, and select the student price—it saves your advisor money. You can ask your advisor’s admin to pay the conference registration directly if you don’t want to wait for reimbursements to be paid back.
Flights: You can book your own flights, or you can use a travel agent, Jerry Constantino. Give the travel agent a budget number to charge—then you don’t have to pay personally and then get reimbursed later. Sometimes the travel agent can find you a good flight, but he sometimes finds one that costs a lot more than what you would have found on your own.
Foreign airlines: When flying from, to, or within the US, please use a United States airline. Federal grants (NSF, DARPA, etc.) will not reimburse for flight legs on foreign-flag carriers that originate or terminate in the US. You can often find the same flight code-shared among both US and foreign carriers. As of 2011, there are exceptions for the EU, Switzerland, Japan, and Australia, but outside these countries foreign-flag carriers will be difficult to reimburse.
Contract fares: The State of Washington has negotiated with airlines for contract fares between Washington and certain destinations. These contract fares are occasionally cheaper than the fares you can get online. The real benefit, though, is that these fares are completely refundable and changeable with no advance purchase, minimum stay, or change penalties. So, they can be worthwhile even if the price is no lower or a smidgen higher than you could get otherwise. The travel agents that UW works with should know about these fares. You can also purchase them yourself from the airline web page.