This is a by no means exhaustive list of significant dates. Please let me know of any that I should add.
Baha’i:
16 Jan. 2011 World Religion Day
21 Mar. 2011 Naw Ruz (Baha’i New Year)
21 Apr. 2011 Start of Ridvan
23 May 2011 Declaration of the Bab
29 May 2011 Ascension of Baha’u'llah
9 Jul. 2011 Martyrdom of the Bab
20 Oct. 2011 Birth of the Báb
12 Nov. 2011 Birth of Baha’u'llah
26 Nov. 2011 Day of Covenant
Buddhism:
19 Jan.2011 Mahayana New Year
3 Feb. 2011 Chinese New Year
15 Feb. 2011 Nirvana Day
19 Mar. 2011 Magha Puja Day
18 Apr.2011 Theravadin New Year
17 May 2011 Buddha Day – Visakha Puja
15 Jul. 2011 Asalha Puja Day
8 Dec. 2011 Bodhi Day
Christianity:
25 Dec. 2010 Christmas
6 Feb. 2011 Epiphany
18 Feb. 2011 start of Week of Prayer for Christian Unity
9 Mar. 2011 Ash Wednesday (Start of Lent)
22 Apr. 2011 Good Friday
25 Apr. 2011 Easter Sunday
2 Jun. 2011 Ascension Day
12 Jun. 2011 Pentecost
27 Nov. 2011 First Sunday of Advent
25 Dec. 2011 Christmas Day
Hinduism:
8 Feb. 2011 Vasant Panchami
3 Mar. 2011 Maha Shivaratri
20 Mar. 2011 Holi
4 Apr. 2011 Ramayana (Hindu New Year)
18 Apr. 2011 Hanuman Jayanti
13 Aug. 2011 Raksha Bandhan
22 Aug. 2011 Krisha Janmashtami
28 Sep. 2011 start of Navaratri
6 Oct. 2011 Dasera
26 Oct. 2011 Diwali
Islam:
16 Dec. 2010 Ashura
28 Jun. 2011 Lailat al Miraj
15 Jul. 2011 Lailat al Bara’ah
1 Aug. 2011 Ramadan begins
26 Aug. 2011 Lailat al Kadr
31 Aug. 2011 Eid al Fitr
5 Oct. 2011 Waqf al Arafa – Hajj Day
4 Nov. 2011 start of Hajj
6 Nov. 2011 Eid al Adha
26 Nov. 2011 Hijra – New Year
5 Dec. 2011 Ashura
Jainism:
15 Feb.2011 Nirvana Day
17 Apr. 2011 Mahavir Jayanti
2 Sep. 2011 Paryushana Parva
22 Oct. 2011 New Year
26 Oct. 2011 Diwali
Judaism:
20 Mar. 2011 Purim
19 Apr. 2011 Start of Pesach (Passover)
1 May 2011 Yom HaSho’ah
8 Jun.2011 Shavuot
29 Sep. 2011 Rosh Hashana
8 Oct. 2011 Yom Kippur
13 Oct. 2011 start of Sukkot
21 Dec. 2011 start of Hanukkah
Sikhism:
5 Jan. 2011 Birthday of Guru Gobindh Singh
13 Jan.2011 Maghi
20 Mar.2011 Hola Mohalla
14 Apr. 2011 Vaisakhi
16 Jun. 2011 Guru Arjan Dev martyrdom
20 Oct. 2011 Installation of Scriptures as Guru Granth
26 Oct. 2011 Diwali
10 Nov. 2011 Guru Nanak Dev Sahib birthday
24 Nov. 2011 Guru Tegh Bahadur martyrdom
Other dates can be found at www.interfaithcalendar.org/