Diary / Planner for Ubuntu?

[D.Sync]

Is there any good and customizable diary and planner for Ubuntu which I can use to enter my daily details and my expenses for that particular day?

[Thisislaw]

Project Management or SimpleAgenda if you like? Maybe TaskJuggler?
Go to Applications > Add/Remove and search for either "Project Management" or "TaskJuggler", or "SimpleAgenda".
http://live.gnome.org/Planner is the site for the Project Management application.

[Redptc]

Evolution has a diary arrangement and it is handy having it linked to your emails.

In fact Evolution is a very good email program....shouldn't be overlooked.

[carandraug]

Mozilla Sunbird (http://www.mozilla.org/projects/calendar/sunbird/) is also quite good.

[TedBuckland]

If you're still searching for a diary, you can also try RedNotebook (http://rednotebook.sourceforge.net).

[weather15]

If you use Mozilla Thunderbird for email there is a calendar plugin I also think it allows you to sync with google calendar and other calendar services. Also if you like google calendar install google gears and install the google calendar offline version.