When I track time, I like to use half days.

A half day is the most meaningful chunk of work progress and, of course, it is flexible - I hate keeping track of quarter hours or worrying about remembering that I stopped to talk to the UPS driver.

I've even written contracts with half days as the basic billing unit - and once I explain to clients that it means I may not bill them for a quick email, they pretty much get it.

I track half days with a pencil and calendar, and write a short description of what I did.

I'm using Yast, cool startup from Norway. I picked this one because it works on desktop and Iphone, possible to add subprojects with different pricing model, share data with another team-members/freelancers, comprehensive reports and has very good API. URL: http://www.yast.com/

I've been using this. Print them out every week. I find them easy to keep track with since I switch tasks often.

http://davidseah.com/blog/node/the-emergent-task-timer/

I love Hamster [1], but since I switched from Linux to the Mac I haven't found anything like it.

[1] http://projecthamster.wordpress.com/about/

I've been giving freshbooks $20/month for the last couple years http://freshbooks.com

http://www.tickspot.com/ is also pretty good. Paid version sync to Basecamp.

I've been pretty happy with toggl.

https://www.toggl.com/

freshbooks.com - time tracking and invoicing in one package.

A pen and notepad

Harvest here

a spreadsheet

manic time