As I've been living in Sheffield for about a year, I can safely say there is always plenty going on, so I doubt you could be bored for long! There are a few annual events that come to the city, and a lot of them are free, which is always welcome.
I'll start by talking about one of the most popular and busy events that Sheffield has on in the Summer, which is the Tramlines music festival. This festival spans across the city, and has various large stages, with bands also playing at some smaller venues such as pubs and clubs. This year the festival will be held between the 20th - 22nd of July, and I would really recommend checking it out if you live close by. In addition to the live music, we usually get a huge fun fair, with plenty of rides (although I think you have to pay for them unfortunately!). The line up for this years festival currently includes Roots Manuva, We are Scientists, Ms Dynamite, and Field Music, as well as a whole host of other bands, so I'm sure there will be something for everyone. The city centre does get exceptionally busy when the festival is on, so if you aren't fond of busy crowds then this might not be for you. If you want to find out a little more, then you can find the website here - http://www.tramlines.org.uk/.
Sheffield also plays host to some lovely international and craft markets that usual visit the city a couple of times a year. We have a Farmers Market which usually takes place on the fourth Thursday of every month, with the next one being held on Thursday the 24th of May. You can buy lots of fresh local produce at this market, with the added benefit of knowing that you are supporting local farmers. This market is situated at the top of Fargate, and runs all day, so I think it is worth checking out if you are in town.
My favourite market is the International Market, which will be coming back to the city from the 3rd - 7th May. I really hope that the weather will improve for it, so I can have a good walk around. This market is on Fargate, and is usually pretty massive so there is a huge selection. We get craft stalls from around the world, selling jewellery and other ornaments. We also get lots of gorgeous food stalls selling everything from Mexican to Chinese, the Indian stand always looks very tasty and the prices aren't extortionate. I would recommend checking out the cakes and sweet stall, and buying one of the huge cupcakes topped with chocolates and other candy!
As I have mentioned in one of my other reviews, Sheffield also hosts the World Snooker Championships which is actually running at the moment. The games are located at The Crucible theatre which is right in the centre of town. It seems that all the tickets are sold out, so if you plan on coming next year, I would advise booking early! If you didn't manage to secure tickets, you might be able to catch a glimpse of some of the players in the Winter Gardens, as they are quite often being interviewed in there.
If you are an art enthusiast be sure to check out Art in the Gardens, a lovely outdoor art and craft festival which is held in the Botanical Gardens. Lots of local artists set up shop there to sell some of their artwork, so I'm sure you could pick up a bargain. The festival is held on the 1st and the 2nd of September, so if the sun is shining, then I think it would make for a great day out.
I hope I've given you some idea about the kind of events Sheffield has to offer, if you have any questions then please feel free to send me a message. I think there's usual an excellent variety of activities for a city that is actually fairly small and compact.
You can find out more details here - http://www.welcometosheffield.co.uk/