Althought it is a lot of work, submission to directories pays in the long run. Especially if you get the backlinks to your site for free.

A great ressource is the list maintained by Dan at http://info.vilesilencer.com/
The list also has a section for niche directories. This comes in very handy for your travel site. Many of the directories in the list are still very new and have a low pagerank, but I can tell you from my experience with the directory at guiding-stars.com, this will soon change. This list drives a lot of traffic to directory sites and the consequence is a higher pagerank soon.

Another place to look is directorycritic. You will find free directories, a listing of niche directories and more.

More ressources:

webdirectory-index

Directory Tracker - here you can also keep track your submissions