Here's a calendar of events in Zagreb for 2010.
(N.B. Any festivals and similar that are mentioned below are usually annual events, and held on roughly the same date each year.)

January
FIS Skiing World takes place in Sljeme (above Zagreb) on 3rd & 6th January 2010, with both men's and women's competitions. See more at Snow Queen Trophy.

February
The Zagreb Indoors tennis tournament is a men's ATP Tour event and usually attracts a smattering of well-known players, as well as (understandably) a reasonably large bunch of the top Croatian players. This year's event takes place from 30th January to 7th February 2010 in its usual home, the Dom Sportova, in west Zagreb.

The Zagreb Wine Gourmet Festival is a two-day event held on 12th & 13th February. It is the largest such festival in Croatia, with over 500 domestic and foreign wines on show.

Depeche Mode are to play the capital at Zagreb Arena on 14th February 2010, in a concert rescheduled from 2009. Tickets can be bought from Ticketpro.

The Zagreb Boat and Sport Show is now in its 19th year, held at Zagreb Fari and with a variety of boat and marine sport exhibitors. It is held over five days, from 24th to 28th February 2010.

March
Zagreb Dox, an international documentary film festival, is in its 6th year this year. Taking place at the MoviePlex in the Kaptol Center, there are several themed programs as well as a competition for the best documentary. It is held 28th February to 7th March 2010.

Leonard Cohen performs at the Zagreb Arena on 15th March 2010. Ticket details here. Now postponed to 25th July.

April
UK band The Editors are to play Aquarius club on 18th April 2010 - a great chance to see them in an intimate venue!

May
Heavy rockers Metallica will perform at the Zagreb Hippodrome on 16th May 2010.

June
Animafest, as the name might suggest, is a world festival of animated film which was first held way back in 1972. This year's festival will be held from 1st to 6th June 2010.

The legendary Bob Dylan is due to play Zagreb Arena on 7th June 2010!

Guns 'n' Roses are also due to play the Zagreb Arena on 20th June 2010.

Lake Jarun is home to the T Mobile INmusic Festival, a two day music event in this pretty setting in southwest Zagreb, with a host of international bands and stars performing. Aside from being held on the weekend of 22nd & 23rd June 2010, details of this year's event are yet to be announced so keep your eyes peeled - last year's line-up included Lily Allen, Moby, NERD and Franz Ferdinand.

C'est is d'Best is a ten-day festival in which street performers - musicians, actors, dancers - take part in various performances in the city. Due to be held 3rd to 13th June 2010.

July
The International Folklore Festival - over the course of five days - brings together folklore groups from Croatia, Europe and even further afield such as France, India, Mexico and the US. Some performances are held on Ban Jelacic square. The Festival takes place 21st to 25th July 2010.

Leonard Cohen performs at the Zagreb Arena on 25th July 2010, a concert rearranged from 15th March. Ticket details here.

August
Another long-standing event in Zagreb is The International Puppet Festival, which has been held every year since 1968. Puppeteers from around the world perform different types of puppet plays at various locations throughout the city. Takes place 28th August to 3rd September 2010.

October
The Zagreb International Chamber Music Festival was only started a few years ago, but already attracts a number of artists. Various classical concerts take place over a week in mid-October.

The Zagreb Film Festival (17th to 23rd October 2010) showcases films from debut or new film-makers from across the world. Prizes are awarded in several categories.