Just like 60's garage-rock, the R&B/soul scene is so full of one-hit-wonders & no-hitters that a question like this can turn into a pissing-match over amazing obscurities. An excellent place to start is the HOT SLOP podcasts available here on this very network.
Me personally, I'm not a fan of the Northern sound, weak and poppy to my ears, and I'm not really crazy about funk; what I like tends to be R&B with a connection to 50's rock or deep soul with heavy-duty wailing vocals. Some fairly common, fairly prolific artists you could pick up on 45.s without busting your trust fund as follows:
WILLIE MABON - sort of a 50's rocker, but more on the black-music tip. Made a bunch of good records.
COASTERS - THEE classic rockin-uptempo-doowop band, can't forget them.
OLYMPICS - Runners-up in the uptempo-doowop category, lotta fun, goofy sorta like the Rivingtons.
ROUZAN SISTERS - Girl-group with a real crude, made-in-the-basement sound, nice rough edged vocals. They only made 4 or 5 records, but when you can find them they're usually pretty cheap and mm-mm-good.
LITTLE JOHNNY TAYLOR - there's two Johnny Taylors, but only the little one interests me. He made a bunch of great 45.s on Galaxy label, real powerful, emotional vocalist.
While you're exploring, don't turn your nose up at church music -- 50's/60's gospel can rock as hard as secular music, you can find some really wild stuff if you look.
Hope this helps --
Hugo M.
pmadreenter@yahoo.com
http://pocamadreenterprises.bravehost.com
NP: blessed silence.