Don't know if ya'll have heard about this website but it's called soultracks.com. They held a poll where thousands voted on the best soul/r&b albums, songs, and artists across several decades.
http://www.soultracks.com/70s-songs
These were the results for the best soul songs for the 70s.
1 What's Going On - Marvin Gaye
2 Let's Get It On - Marvin Gaye
3 Let's Stay Together - Al Green
4 If You Don't Know Me By Now - Harold Marvin and The Blue Notes
5 Just My Imagination - The Temptations
6 Me and Mrs Jones - Billy Paul
7 Mercy Mercy Me - Marvin Gaye
8 Didn't I Blow Your Mind This Time - The Delfonics
9 Theme From Shaft - Issac Hayes
10 Midnight Train To Georgia - Gladys Night and The Pips
11 Rock With You - Michael Jackson
12 Papa Was a Rolling Stone - Temptations
13 Wake Up Everybody - Harold Melvin and the Blue Notes
14 You Make Me Feel Brand New - Stylistics
15 Distant Lover - Marvin Gaye
16 Where Is the Love - Roberta Flack and Donny Hathaway
17 Superfly - Curtis Mayfield
18 Close the Door - Teddy Pendergrass
19 Love Train - O'Jays
20 Loving You - Minnie Riperton
21 Have You Seen Her - Chi-Lites
22 For the Love of You - Isley Brothers
23 Always and Forever - Heatwave
24 Use Ta Be My Girl - the O'Jays
25 One Nation Under A Groove - Funkadelic
26 Backstabbers - O'Jays
27 In the Rain - The Dramatics
28 Killing Me Softly - Roberta Flack
29 Tell Me Something Good - Rufus
30 I'll Be Around - Spinners
31 Living for the City - Stevie Wonder
32 I'm Still in Love with You - Al Green
33 Betcha By Golly Wow - Stylistics
34 Don't Stop Til You Get Enough - Michael Jackson
35 Got to Give it Up - Marvin Gaye
36 You Know How to Love Me - Phyllis Hyman
37 Off The Wall - Michael Jackson
38 Oh Girl - Chi-Lites
39 What You Won't Do For Love - Bobby Caldwell
40 Ain't No Stoppin' Us Now - McFadden and Whitehead
41 Family Affair - Sly and the Family Stone
42 For the Love of Money - O'Jays
43 I Want You - Marvin Gaye
44 We Are Family - Sister Sledge
45 Shining Star - Earth Wind & Fire
46 Love Don't Love Nobody - Spinners
47 That Lady - The Isley Brothers
48 Easy - Commodores
49 I'll Take You There - Staples Singers
50 Love Won't Let Me Wait - Major Harris
51 Best of My Love - The Emotions
52 September - Earth Wind & Fire
53 The Ghetto - Donny Hathaway
54 Thin Line Between Love and Hate - The Persuaders
55 You'll Never Find Another Love Like Mine - Lou Rawls
56 Got to Be Real - Cheryl Lynn
57 Kiss and Say Goodbye - The Manhattans
58 Shame - Evelyn Champagne King
59 Rapper's Delight - The Sugarhill Gang
60 Free - Deniece Williams
61 This Masquerade - George Benson
62 Happy Feelin's - Maze feat. Frankie Beverly
63 Lady Marmalade - Labelle
64 Walk Away From Love - David Ruffin
65 Love On a Two Way Street - The Moments
66 Strawberry Letter 23 - Brothers Johnson
67 Street Life - The Crusaders feat. Randy Crawford
68 I Wish - Stevie Wonder
69 Float On - The Floaters
70 Lean on Me - Bill Withers
71 Natural High - Bloodstone
72 Pick Up the Pieces - Average White Band
73 Wildflower - New Birth
74 Ain't No Sunshine - Bill Withers
75 Can't Get Enough of Your love - Barry White
76 It's a Shame - The Spinners
77 Good Times - Chic
78 Everybody Plays The Fool - The Main Ingredient
79 Isn't She Lovely - Stevie Wonder
80 Sideshow - Blue Magic
81 Someday We'll All Be Free - Donny Hathaway
82 I'll Be Good to You - Brothers Johnson
83 Smiling Faces Sometimes - The Undisputed Truth
84 O-o-h Child - The Five Stairsteps
85 Play That Funky Music - Wild Cherry
86 Brick House - Commodores
87 Flashlight - Parliament
88 Ladies night - Kool and the Gang
89 You're Still a Young Man - Tower of Power
90 War - Edwin Starr
91 This Will Be - Natalie Cole
92 Walking in Rhythm - Blackbyrds
93 What A Fool Believes - Doobie Brothers
94 I Wanna Get Next to You - Rose Royce
95 Show and Tell - Al Wilson
96 Fantasy - Earth Wind & fire
97 Reunited - Peaches & Herb
98 Still Water (Love) - The Four Tops
99 Feel the Fire - Peabo Bryson
100(T) Higher Ground - Stevie Wonder
100(T) The Love You Save - The Jackson 5
This is a pretty damn good list. Accurate too.