Few more thoughts, following HistoryDigger and DrFumblefinger...
1. Definitely check all your affiliations on car rental; after years of getting better price through AAA than any other way I knew, I recently found that going to the same vendors through USAA (my car insurance) gets me even better.
2. Not only does Priceline have good pricing on cars, I've often found I can get 30-40% lower through their blind-bidding (Name Your Own Price) service.
3. RailEurope is something of a red flag for me. Not only are they almost always the highest-price vendor compared to direct booking with the railroads, they also don't list all the discounts and sometimes not even all the trains...and they don't make delivery too easy, either. Unless you find a railpass that's a really good price point for you, you're most often better off booking directly, online, and printing out your tickets--which come with reservation where necessary and generally don't require validation because the time, date, train and seat are printed directly on them.
Mark Smith's seat61.com, by the way, is super-helpful, with details of nearly every route and strategy. On my present trip, the rail leg between Vienna and Prague is costing us 22 euros; RailEurope wanted 44. Mark's advice included another saver: buying the tickets from the Austrian rail system, the would have cost 33 euros, but the Czech railroad sells the ticket for 22. Same train, same day, different price!