I have a few different tips that I find save me a bucketload on my travels!
Communications:
FREE WI-FI - I can't stress that enough! If you can, plan where you'll have wi-fi access before you travel so that you don't waste time looking for it over there. Good examples are at airports (either in the terminal if you're lucky, or for most of us here, in the lounge), hotels (sometimes it's free in the lobby for all guests, though I always get it for free in-room as HHonors Gold (and this is one of the major reasons that I stay in their hotels)), and cafes/fast foods outlets. To this regard, I would never be seen without my iPhone overseas! For SMS messages to fellow iPhone users, iMessage makes it free when on wi-fi, and to all other users, I use an app called SMSPup (which is linked to
Free SMS Australia, download ringtones & mobile phone games). It uses your phone's data connection (eg. wi-fi when you have roaming data disabled), and allows you to send real SMS messages to any Australian mobile phone. As the messages are technically sent from their end and not from your phone, there is no charge on your phone bill, and the recipient gets an advertising-free message that looks exactly like it was sent from your phone (it uses your number as the 'caller ID' on the message). Each message costs one 'point'. You can earn 'points' by clicking on advertising links in emails that they send you (I don't use my primary email for this obviously, though the emails aren't excessive). On my Dec/Jan 2010/11 trip to Europe, I spent about $450AUD on roaming (mostly data and SMS) for a 3 week trip - which was before my iPhone. Once getting my iPhone and doing this trick with the wi-fi, my roaming bill from my last 6-week trip to Europe was $0.

For free calls, there is always Skype - which again can be used over wi-fi, and doesn't need a computer/laptop (and there's a Skype app on iPhone, Android and Nokia - probably others too).
Attractions and landmarks:
If you have a student card, it doesn't hurt to take it with you abroad! I have received many discounts on presenting my Australian university ID, despite it not being the 'International Student Identity Card' that you can also pay to get. While it generally won't work for public transport discounts, most places that quote a student rate will happily oblige... once such place from memory is admission to Westminster Abbey in London. I also usually never even get any funny looks when handing over a platinum Amex card after presenting my student ID
Hotel rates:
Be flexible with your dates, and when you've made up your mind, lock them in with an advance purchase rate (provided you know that your plans won't change). AP rates typically offer up to 30% off the best available rate, and if pre-paid, also usually bypass any credit card surchages that might be in place at some hotels. Also, it's usually always best value to book directly with the hotel that you are planning to stay at, instead of any third-party booking sites - which usually add their own fees even if they pass the same rate along. It also doesn't hurt to join the applicable loyalty program if you are staying in a property (or properties) belonging to a particular chain. If you stay enough, you can earn benefits such as free breakfast, wi-fi and upgrades. You could also slowly save up your hotel points in such a program to redeem for one free night, and many discount rates are only available to members (such as Rydges' Priority Guest members rates)... especially useful when there's no joining fee!
Food:
If you have a free breakfast included at your hotel (or can get it for a reasonable price), by all means utilise it! You can even be sneaky by heading to the buffet around 9:30am (for a breakfast that finishes at 11am), eating a full breakfast, sitting for a while with a coffee, and then having an early lunch from the same buffet before leaving. Still counts as your 'free breakfast', but you also get an early lunch out of it if you're really trying to cut costs

If you also have access to the Hilton Executive Lounge (or similar), having a free nibble early in the evening can save you having to buy an entre if you're dining out that night - you can head straight for the main course!
Currency and cards:
I always pre-purchase my currency before travel - usually from Westpac's FX4YOU (unless they don't stock the currency I'm after). The conversion rates used are respectable, and it allows BPAY payment from a credit card as a 'purchase' (eg. your bank doesn't treat this as a cash advance, so if your card earns frequent flyer points on BPAY purchases, you will earn those on the $AUD amount spent on forex). While it may be slightly more expensive than converting $AUD into local currency overseas, I see it as good value - as I earn points on the total (which I value at around 6c each - earning 625 per $1000 spend on MasterCard BPAY brings an added value of 3.75% despite the difference in currency rate), and there's also the convenience factor of having everything organised before you depart. As others have said, for cards, you can't go wrong with the 28 Degrees MasterCard... I don't use it myself (I value my points higher than the forex fees charged when using my Amex), but if you're really trying to minimise costs, it's great! Also, Dynamic Currency Conversion (where you are given the option to be charged in your home currency on Visa/MasterCard- eg. $AUD when abroad) is an absolute rort. It pads the exchange rate by 1.5%, and although your card is then charged in $AUD, many Australian banks have a 'cross-border processing fee' (essentially a fee for a foreign transaction, regardless of the currency). You are *much* better off just charging the amount in the local currency.
Travel insurance:
No insurance? Don't travel. Simple as that. Many premium credit cards have complimentary travel insurance included as one of the benefits, though if you plan on using it, make sure you meet the requirements. If you're sneaky and have multiple cards with insurance benefits, you can always qualify for insurance benefits on multiple cards for the same trip, just in case the PDS differs slightly between the cards. As an example, my CBA Diamond cards require ~$1000AUD of pre-paid travel expenses be charged to the card before departure to activate insurance protection. Such expenses include not only flights, but also hotel pre-payments, attractions, cars, concert tickets, etc etc... Conversely, my Westpac Earth Platinum Plus card requires that the return airfare be charged to the card (eg. no protection if you only use it to pay for hotels). As the WBC card earns bonus points on Qantas transactions, I use it to pay for the flights, and the CBA card to pay for the hotels... two free insurance policies as well as bonus points - hard to beat!

Also, for cardholders that have 'rental vehicle excess' cover, beware that there is no concept of 'excess' in the USA, which makes the coverage provided under these policies worthless... be sure to get the insurance from the hire company, as a small expense pre-rental can save thousands post-rental.
That's about it!
