I know this is less programming related and more time management related, but I value the feedback of the users on this site. I\'m finding myself particularly busy this semester
Backpack is a good one from 37signals. They have free accounts, multiple users and an API. I am not sure about SVN access though.
You also might think about TRAC. It plugs in well with SVN, and although is made more for development, it would work well for your needs I think.
Update: You mentioned that Trac is geared towards teams, and while true, I don't think that is really a bad thing. I don't think there are any features in it that really require multiple users or that would slow you down from using it on your own. And if you ever need to collaborate with someone else it will already be set up to do it.
Try rememberthemilk. Good tool and has number of useful interfaces.
http://www.redmine.org/
Use the Tasks in GMail. They are useful, prett ylightweight, you can have a hierarchy of tasks. Good if you are already using GMail.
There is also a Remember The Milk plugin for GMail. Here you can't have sub-tasks, but it's pretty good too, all in all.
Nobody has mentioned SlimTimer yet (www.slimtimer.com). This is a slick little web tool that is very flexible and easy to use.
The best part IMHO is that each task has a display name in your task list as well as 0..n tags that you can use for reporting. This way, my to-do list has simple names that I can relate to, and each task is tagged with the corresponding project identifier that I must report my time on.
My SlimTimer keeps track of my time spent each day or week, and when I feel like it, I pull up a report and fill the data into my company billing system.
http://www.myhours.com/
Track your work, your private projects, calculate costs, send reports by email and more. Follow 3 easy steps to start time tracking: