Just looking at Woo Themes today and noticed they have a couple of really nice wordpress themes for travel sites.
1) City Guide by WooThemes – This would suit any affiliate that wants to make a city guide. Comes in 6 styles and features an integrated Google Maps functionality for use in posts as well as a sidebar widget.
2) Postcard by WooThemes – aimed at travel bloggers, this wordpress theme also features geo tagging for Google maps. The cute bit about this theme is the homepage slider styled to look like the front and back of a postcard.
Update : How about this great city directory theme “Geo Places by Templatic”. Like the woo themes, this is integrated with Google Maps, Geo-Places comes with colour scheme options, is all set up for user reviews and even offers the opportunity to take paid listings, e.g. for hotels, restaurants and events. The theme has support for all the main payment gateways.