MM wrote this post of festivals and I realised while reading the comments that there were so many things I wanted to add myself. I did too but then there was more so here goes.
There are so many small festivities in Karnataka we celebrate apart from Sankranthi (Pongal), Ugadi,Ganesh Chaturthi and Deepavali.
Bheemana amavasya - It falls on the amavasya day - beginning of ShravaNa month. It is a pooja for Lord Shiva who is the God of Death for the long life of the husband/wouldbe husband. But I've also heard people tell that it is a prayer that Goddess Parvati did to get her dream husband (ie; Shiva) and so all unmarried girls do this pooja to get a good husband! It is similar to Karva Chaut in the only way that it is a prayer for husband's long life but contrary to KC - there is no seeing the moon (its Amavasya!) and no fasting :-) Infact goodies are made as Naivedya to the God... Oh! And then if you have a brother he breaks a small piggy bank made of flour which will contain some small change though I dont know the significance of this.
Naga Panchami - This is a worship to the Snake gods to keep the brothers in the family healthy and happy. We offer steamed kadabu (modak) and milk to the God as offering that day.Generally the sisters gift something to the brothers on this day. And oh! We also dab a little milk and ghee on the stomach and back of the brother - a symbol of bathing in milk and ghee to wish him good health and wealth! It used to be fun as Bro would always scream that it was cold :-D
Varalakshmi vrata - Pooja to the goddess Lakshmi similar to what is performed during Diwali. A saree is draped and the face of the Goddess is dressed up with false hair/bindi/ hands are made rolled out of blouse pieces and bangles are put around them and ofcourse OBBaTTu is the sweet (similar to Pooran PoLi).
MangaLa Gauri Vrata - Not sure how many people would have even heard of this - Done by newly married women for the first 5 years of their marraige for a happy married life on 4/5 tuesdays of theShravaNa month.
Swarna Gauri Vrata/Ganesh Charuthi - The story goes that Gauri along with her son Ganesh comes to the mother's house for a holiday :-) And Ganga is their mode of transportation. So we first do pooja to Ganga ( a well in Mom's house) and then bring them in. Do the Gauri pooja and Ganesh pooja and then Visarjan when we send them back to their abode - again through Ganga :-) A point to be noted is that we send some food (generally sweetened/curd poha) for their onward journey. Also, the day after the Visarjan we still prepare goodies and special food because another story goes that Lord Shiva, after listening to GAuri and Ganesh about all the yummy food they ate, festivities they had - decides to see for himself what all the furore is. And he is the Son-In-Law - so he also has to be treated well too! Listening to all these stories makes them one of us - isnt it? And so bro and me always enjoyed this festival the most. Oh! And we give 'baagina ' to the ladies which includes all types of Dal/Rice/Jaggery and fruits along with the usual Haldi/kumkum.
Navaraatri - Bombe Habba as it is called. It is more famously called Gollu in Andhra/Tamil Naadu but mostly pooja is done to the various Goddesses for the 9 days including the Pattada Bombe - wooden Man and Woman toy that is given during one's wedding and dressed in finery. It is considered as Lakshmi Venkateshwara. Also, on the Durga ashtami day haldi kumkum is given to Kanya Muthiade - Pre pubescent girls. And its so much fun to watch it.
Oh and I shouldnt forget to add this - All Vrata's have a symbol of tying a yellow thread around the writst to indicate that one has successfully done the pooja. If the husband is present the thread is generally tied by him :-)
Another point to note is unlike in North India where most of the poojas insist that one has to starve, in the south we generally have a feast for all the festivities :-) which adds to more fun.