Justin Bieber remains an immutable force of Twitter trend power, taking the top slot again for the third week in a row. Tweeters also showed their love (and/or disdain) for a number of other pop singers, and celebrated a few holidays this past week.

Thanks to our friends at What The Trend, we have yet another interesting stats-eye-view of the Twitterverse. Because this is a topical list, hashtag memes and games have been omitted from the chart below.

Beyond Justin Bieber, Follow Friday, and Music Monday — the reigning trend champs — St. Patrick’s Day made an appearance as people tweeted their revelry, and Lady Gaga crept up on the list with the premiere of her new video on Vevo and a tour in New Zealand.

The Jonas Brothers hung tight near the middle, while circle enthusiasts everywhere tweeted vigorously about Pi Day on March 14th, spurred on no doubt by the charming Google doodle that commemorated the occasion.

If you own a TV or computer, you probably know that March Madness is upon us, and bracket-related tweets have been flying around the web all week, landing the term at number seven.

Rounding out the chart are two more singers who made some news this week. Demi Lovato, the 17 year old actress/singer, stirred some buzz with her admission that she’s dating a Jonas Brother, and Chris Brown, the career-stunted R&B singer, reached out to his fans on the web for some help on making a comeback.

Strangely, tweets about the ongoing South By Southwest (SXSW) conference — one of the most talked about topics in tech and a favorite of the Twitter community — did not reach critical mass to make this week’s list. This is likely due to the lack of big announcements or product launches from the conference this year.

You can check past Twitter trends in our Top Twitter Topics section as well as read more about this past week’s trends on What The Trend.

Top Twitter Trends This Week 3/13 – 3/19
RankTopicTop Index This WeekChangeDescription#1Justin Bieber1Justin Bieber’s new album My World 2.0 comes out on March 23rd & his fans are excited. He also appeared on Z100.com, QVC, and GMTV in the UK.#2Follow Friday1Follow Friday is a tradition where people tweet people they believe are fun/interesting to follow (on Fridays).#3St. Patrick’s Day2NEWPeople are tweeting "Happy St. Patrick’s Day" and showing their Irish spirit.#4Lady GaGa22Lady GaGa is currently touring in New Zealand.#5Music Monday2Music Monday is a tradition where users recommend music they appreciate every Monday.#6Jonas Brothers7Mentions of the Jonas Brothers.#7March Madness1The National Collegiate Athletic Association’s Division 1 Men’s Basketball tournament started this week.#8Happy Pi Day2NEWMarch 14th is Happy Pi Day! Pi is, roughly, 3.14. And today is 3/14. And March 14 is also the birthday of Albert Einstein#9Demi Lovato3March 13 2010, "Jemi" is confirmed. Demi Lovato admitted to dating Joe Jonas in an interview by Billy Bush. Many people are tweeting their opinions about this new couple. Joe Jonas and Demi also recently released a new song, "Make a Wave."#10Chris Brown1NEWSinger Chris Brown asked his fans to help revive his
career. They have been obliging with a variety of trends.

Tags: justin bieber, Top Twitter Topics, trends, twitter, twitter trends, What The Trend