Suttas by Theme (more to be added over time...)
(yet to go through AN4.201 onwards or most KN theme references...)
The below is by no means exhaustive and merely serves to provides examples. Numerous suttas contain multiple themes.
Agitation - Sn5.2
Anger - AN2.180-229, AN4.43, AN4.44, AN4.84
Appearance - AN4.65
Aspiration - AN2.130-140, AN4.176
Assemblies - AN2.42-51, AN3.95
Attainment - AN2.163-179
Austerity - DN25
Awakening - AN3.103-112
Awakening Factors - SN46
Bad Teachers - DN12
Becoming - Sn5.3, Sn5.4, Sn5.5
Birth - Sn5.3, Sn5.4, Sn5.7, Sn5.10, Sn5.11, Sn5.16
Body - SN43.1
Brahmins - AN3.51-60
Causation - DN15
Clairaudience - DN2
Clairvoyance - DN2
Clinging - Sn5.4, Sn5.5, Sn5.12
Concentration - DN10
Conduct - DN31
Confidence - AN4.34
Consciousness - DN9, DN15, Sn5.4, Sn5.6, Sn5.13
Contact - SN36.10
Contentment - AN4.27, Sn5.2, Sn5.5
Craving - AN4.9, AN4.199, DN15, MN6, MN11, MN37, MN38, SN12.52 - SN12.57, SN18.8, SN23.2, SN38.10, Sn5.1, Sn5.2, Sn5.4, Sn5.5, Sn5.6, Sn5.7, Sn5.8, Sn5.9, Sn5.12, Sn5.13, Sn5.16
Death - AN1.616-627, Sn5.3, Sn5.6, Sn5.11, Sn5.12, Sn5.16
Deathless - SN47.41, Sn5.5, Sn5.8, Sn5.10, Sn5.14, Sn5.15
Defilements - DN2, SN12.23, SN27, SN38.8
Dependent Arising / Dependent Origination - AN3.61, DN15, MN9, MN28, MN38, MN74, MN75, MN115, MN146, SN12
Desire - SN23.23, SN23.34, SN27.1 - SN27.10, Sn5.1, Sn5.2, Sn5.3, Sn5.4, Sn5.6, Sn5.7, Sn5.8, Sn5.9, Sn5.11
Diligence - AN4.116, SN3.17, SN47.63
Disciplinary issues - AN2.11-20
Doubt - DN6, MN16, Sn5.5, Sn5.9
Eating meat - MN55
Eightfold Path - DN6, DN8, DN22, DN23, MN2, MN9, MN43, SN14.28, SN45
Elements - MN28, MN140, SN14, SN18.9
Emptiness - MN121, MN122, SN43.4
Energy - AN1.61-70
Equanimity - Sn5.13
Ethics - AN4.12, AN4.136, AN4.137, DN10, DN12, SN47.21, Sn5.7
Factors of Enlightenment - SN43.10, SN46
Faculties - AN4.151, DN16, MN77, MN152, SN9.13, SN43.8, SN48
Faith - SN10.9, SN10.10, SN10.11, SN25.1 - SN25.10
Fearless - AN4.184
Feelings - MN43, MN59, SN14.4, SN14.5, SN18.5, SN36, SN38.7
Fetters - AN4.88, AN4.131, DN13, MN16, MN64, SN41.1
Five Aggregates - AN4.90, DN6, MN28, MN35, MN38, MN43, SN18.10, SN18.21, SN18.22, SN22, SN23
Five Hindrances - AN1.11-20, DN2, DN5, DN6, DN13, MN27, MN39, MN48
Five Powers - SN50
Five Precepts - SN14.25
Flood - Sn5.1, Sn5.10, Sn5.11, Sn5.12
Fools - AN2.21-31, AN2.98-117, AN3.1-10
Four Elements - AN4.177, SN14.30, SN14.33, SN14.37 - SN14.39
Four Noble Truths - DN2, DN7, DN16, DN22, DN27, MN28, MN77, MN141, SN12.27, SN13, SN36.26, SN56
Foundations of Mindfulness - DN22, MN10, SN47
Giving - AN2.141-150
Going for Refuge - SN40.10
Good Friends - AN1.71-81, SN3.18
Good Teachers - DN12
Gradual Training - AN10.99, DN2, DN3, DN4, DN5, DN6, DN7, DN8, DN9, DN10, DN11, DN12, DN13, MN27, SN16.9 (for more detailed information, see Leigh Brasington)
Grasping - SN22.7, SN22.8, SN38.12
Guilt - AN4.121
Happiness - AN2.64-76
Hard Work - SN47.73
Heedlessness - Sn5.1, Sn5.4, Sn5.16
Hell - AN4.64
Hindrances - See Five Hindrances above
Ignorance - SN20.1, SN38.9, SN45.1, Sn5.1, Sn5.13
Imperfections - MN128
Impermanence - DN17, MN22, MN23, SN22.12, SN22.15, SN22.102, SN23.13, SN23.14, SN35.1 - SN35.12, SN36.9
Immersion - AN4.41, AN4.92, AN4.93, AN4.94, SN22.5, SN36.1
Impossible - AN1.268-277, AN1.278-286, AN1.287-295
Inclusion - AN4.32
Intention - AN4.171, SN12.38, SN12.39, SN12.40, SN18.7
Jhānas - AN4.124, AN9.36, AN9.39, DN2, DN5, DN9, DN22, MN8, MN19, MN25, MN43, MN44, MN77, MN52, MN53, MN59, MN64, MN66, SN16.9, SN21.1, SN34, SN36.11, SN40.1 - SN40.8, SN53
Kamma - MN45, MN46, MN56, MN57, MN70, MN135, MN136
Lazy - SN14.22
Learning - AN4.6
Liberation - Sn5.6, Sn5.9, Sn5.12, Sn5.13, Sn5.14
Lives of past Buddhas - DN14
Love - AN4.125, AN4.126, SN20.4 - SN20.5
Magic - SN42.13
Mara - DN16, DN25, MN25, MN34, MN49, MN50, MN119, SN4, SN5.1 - SN5.10, SN23.1 - SN23.22, SN35.65, Sn5.10
Meditation - DN22, MN34, MN62, SN43.5, SN47
Men - AN1.1-10
Metta - MN48
Mindfulness - DN5, DN6, MN10, SN10.4, SN43.1, SN43.5, SN47
Mindfulness in/on/of the Body - AN1.575-615, MN119, SN43.1
Mindfulness with/of Breathing - DN22, MN118, SN54
Negligence - AN1.82-97, AN1.98-139
Noble Search - MN26
Non-offense - AN1.150-169
Not-Self - SN22.11, SN22.14, SN22.17, SN22.20, SN23.17, SN23.18
Nuns - SN5, SN19.18, SN19.19, SN19.21
Old Age - AN4.119, SN1.51, SN3.3, SN12.71, SN16.5, SN22.1, Sn5.3, Sn5.4, Sn5.7, Sn5.10, Sn5.16
Other religions - AN3.68
Peaceful mind - AN2.32-41
Perceptions - SN14.7, SN18.6, Sn5.6
Powers - SN37.25 - SN37.34, SN43.9, SN50
Precepts - AN4.81, DN1, DN5, DN32, MN76
Prejudice - AN4.17, AN4.18, AN4.19
Psychic Powers - DN2, DN10, SN5.5, SN41.4, SN43.7, SN51
Punishments - AN2.1-10
Recollection of past lives - DN2
Restraint - AN4.14
Right Action - DN22
Right Concentration - DN22, MN36
Right Effort - AN4.13, AN4.69, AN4.71, DN22, MN49, SN43.6, SN49
Right Speech - AN4.149, DN22, MN41, MN42, MN58, SN8.5, SN11.5
Right View - AN4.72, AN4.89, MN8, MN9, MN38, SN12.15, SN22.51
Rite & Rituals - SN42.6, Sn5.3, Sn5.7
Seclusion - AN3.93, SN9.1, Sn5.5
Sense Contact - SN18.4
Sense Consciousness - SN18.3
Seven Elements - SN14.11
Sex - AN1.1-10, AN4.159, AN7.50, Snp4.1, Snp4.7
Shameless - SN14.19
Sickness - Sn5.3
Signless - SN41.7
Six Sense Bases - MN137, MN149, SN35
Skilfulness - Sn5.1
Spiritual Life - AN4.25, Sn5.2
Stream Entry - MN53, SN24.1 - SN24.18, SN55
Subtlety - AN4.16
Suffering - MN1, SN12.26, SN12.43, SN12.51, SN22.13, SN22.16, SN22.19, SN23.15, SN23.16, SN38.14, SN42.11, Sn5.1, Sn5.4
Taking on Practices - MN45, MN46
Ten Powers - MN12, SN12.21, SN12.22
Tendencies - SN18.21
Thirty two marks of a great man - DN14, DN30
Thoughts - MN20
Three Characteristics - SN18.1 - SN18.20
Three Poisons - SN42.1
Three Knowledges - DN13
True Individual - AN4.73, DN27
True Man - MN113
Twelve defilements - MN40
Unconditioned - SN43
Undeclared - SN44
Unethical - SN14.24
Unskilful Thoughts - SN9.11
Unthinkable - AN4.77
Useless Mind - AN1.21-30
Wild Mind - AN1.31-40
Wisdom - DN1, DN4, DN10, DN11, Sn5.1, Sn5.9, Sn5.11
Women - AN1.1-10, SN17.21, SN17.22, SN37
Wrong speech - AN4.82, AN4.148, MN41, MN42, MN58
Wrong view - DN1, DN12, DN23, DN24, MN8, MN72, MN76, SN35.165
Yokes - AN4.10
The Buddhas Disciples
Ānanda - AN3.32, AN3.71-80, AN4.129, AN4.159, AN4.174, DN10, DN16, DN17, DN18, MN18, MN132, SN16.10, SN16.11, SN22.21, SN22.37, SN22.38, SN28.1 - SN28.10, SN44.10
Aṅgulimāla - MN86
Anuruddha - MN31, MN68, MN127, SN16.6, SN52
Bhaddiya the Dwarf - AN4.193, SN21.6
Devadatta - AN4.68, MN29, SN17.31 - SN17.36
Godatta - SN41.7
Kassapa - DN8, SN16.1 - SN16.13, SN41.9
Kassapagotta - AN3.91
Khemā - SN44.1
Kimbila - MN31
Kumāra Dassapa - DN23
Mahācunda - MN8
Mahaka - SN41.4
Mahākaccāna - MN18, MN133, SN22.3, SN22.4
Mahākappina - SN21.11, SN21.12
Mahākoṭṭhita - AN4.173, AN4.174
Moggallāna - AN4.167, AN4.168, DN17, MN5, MN15, MN37, MN50, MN108, SN19.1, SN21.1, SN21.3, SN40, SN44.7
Nanda - SN21.8
Nandiya - MN31
Rādha - SN23.1 - SN23.3, SN23.11 - SN23.46
Rahula - AN4.177, MN61, MN62, MN147, SN18
Sāriputta - AN3.33, AN4.167, AN4.168, AN4.172, AN4.173, AN4.175, DN17, DN28, DN33, DN34, MN3, MN5, MN9, MN24, MN28, MN43, MN69, SN16.12, SN21.2, SN21.3, SN22.2, SN28, SN38.1 - SN38.16, SN39.1 - SN39.16, SN44.3 - SN44.6, SN45.3
Sujāta - SN21.5
Tissa - SN21.9
Udāyi - MN59
Royalty interacting with the Buddha
King Ajātasattu - DN2
King Bimbisāra - Snp3.1, Vin.i.35ff
King Pasenadi - MN24, MN86, MN87, MN88, MN89, MN90, SN3.1-SN3.25, SN44.1
King Vessavana - DN32
Prince Abhaya - MN58
Prince Ajātasattu - SN17.36
Prince Hatthaka - AN3.35
Prince Sunakkhatta - DN24
Queen Mallikā - AN4.197
Others
Alāra Kālāma - MN26
Ambaṭṭha - DN3
Brahmā Sahampati - SN6.1, SN6.2, SN6.3, SN6.12, SN6.13
Citta - SN41
Cunda - DN16
Jambukhādaka - SN38
Kālāmas (The) - AN3.65
Mahāvīra / Nigaṇṭha Nātaputa - DN2, DN29, DN33, MN56, MN58, SN41.8
Nigrodha - DN25
Sakka - DN19, DN21, MN37, SN40.10
Sāmaṇḍaka - SN39
Sarabha - AN3.64
Uddaka Rāmaputta - MN26
Upāli - MN56
Vacchagotta - AN3.57, MN71, MN72, MN73, SN33, SN44.7 - SN44.11