Ubuntu has long accepted donations for the project, but now they have made it more apparent with changes to the Ubuntu web-site.
When going to download Ubuntu, there's now a "contribute screen" that is displayed as part of the download process where they can financially donate to Canonical. In hopes of not alienating people, for those making donations they can choose how their donation should be spent.
Among the options for the donation are working on the desktop, performance optimizations, improving hardware support, phone/tablet Ubuntu, community participation, better coordination with Debian and upstream, better Ubuntu derivative support, or just a tip to Canonical. They were reportedly inspired by the Humble Indie Bundle with this method of choosing how the money is to be used.
When going to download Ubuntu, of course, users can opt to make no donation at all and just proceed with the download.
This change was mentioned on the Canonical Blog and Jono Bacon also wrote about this as Easier Financial Contributions To Ubuntu.
If you're looking to be a patron, you can also make a PayPal tip or subscribe to Phoronix Premium for advancing the Linux hardware benchmarking and performance monitoring done at Phoronix along with the hundreds of news stories that are single-handedly written by myself each month on Phoronix.com.