I sometimes read that Lord Ganesha's wives were 'Siddhi' and 'Buddhi' and sometimes 'Riddhi' and 'Siddhi' and also sometimes that all 3 'Riddhi', 'Siddhi' and 'Buddhi' were his wives.
Lord Ganesha is married to Siddhi and Buddhi:
ब्रह्मा उवाच:
एतस्मिन्नन्तरे तत्र विश्वरुपः प्रजापति ।
तदुद्योगं संविचार्य सुखमाप प्रसन्नधि ।।
विश्वरुपप्रजेशस्य दिव्यरुपे सुते उभे ।
सिद्दिबुद्धिरिति ख्याते शुभे सर्वांगशोभने।।
ताव्या चैव गणेशस्य गिरिजा शंकरौ प्रभू ।
महोत्सावं विवाहं च कारयामासतुर्मुदा ।।
सन्तुष्टा देवता सर्वास्ताद्विवाहे समागमन् ।
यथा चैव शिवस्यैव गिरिजाया मनोरथ ।। ( Shiva Purana, Rudra Samhita chapter 20)
Brahma said "In the meantime Prajapati Vishwarupa had two daughters possessing divine features known as Siddhi and Buddhi. All the limbs of their body were extremely beautiful. The marriage of Ganesha was fixed with them by Shankara (Shiva) and Girija (Parvati). All the Gods joined the marriage party delightfully, in the same way as desired by Shiva and Girija (Parvati)."
Riddhi and Siddhi were only two wives of Lord Ganesha. Here is a story about the marriage of Lord Ganesha.
On hearing Ganesha's intelligent words, Shiva and Parvati were pleased and at once decided to celebrate His marriage first. Prajapati Vishwaroopa's two beautiful daughters, one called Riddhi and the other called Siddhi, were selected to marry Lord Ganesha. The divine sculptor Vishwakarma made all the arrangements for the marriage by constructing a beautiful marriage hall. Lord Shiva and Parvati celebrated the marriage of Ganesha to Riddhi and Siddhi, who bore Him two beautiful sons named Labha and Kshema respectively.
Here is a mention in shiv purana about Riddhi and Siddhi the two wives of lord ganesha and there sons too.
Even half way through the full circle of the World, Sage Narada intercepted Kartikeya and conveyed that Ganesha’s wedding with Siddhi and Riddhi was in progress already (they were blessed with two sons Kshema and Labha eventually)
so a few things we get here
Eshan has given a good answer.I am just adding on to his one.Lord Ganesha has many other wives too wives.They are:
1)Tushti, Pushti and Shri. You can get some information on them here
2)Kshemadayini.From the mantra used for tarpanam "Kshemadayini sahitam Vighna rajam Tarpayami" Kshemadayini is Vighnaraj's shakti or consort whatever you may like to say. source:Who are the consorts of Vishnu,Ganesha and Saraswati?
3)Kola Bo.In Bengal, Ganesha on Durga Puja is associated with a plantain (banana) tree, the "Kola Bo" (also spelled Kalobou or Kolabau), ritually transformed into a goddess during the festival.You can get more information on here
