Sir's 28 May 98 - 11:45 PM post is how I remember singing this song in my Black Baptist church in New Jersey (at least the 1960s and on).
The song had a moderately slow tempo.

Here are the words as I remember them:

Bless the Lord, Oh my soul
And all that is within me
Bless His Holy Name

Bless the Lord, Oh my soul
And all that is within me
Bless His Holy Name

He has done great things
He has done great things
He has done great things
Bless His Holy Name
{Repeat entire verse 1x)

Bless the Lord, Oh my soul
And all that is within me
Bless His Holy Name

Bless the Lord, Oh my soul
And all that is within me
Bless His Holy Name

Here are links to three YouTube videos of African American choirs/groups singing "Bless the Lord O My Soul". The first link is the closest to the way I remember this song being sung.

http://www.youtube.com/watch?v=FPIaplJPayQ&feature=related

Talented-Bless The Lord (Oh My Soul)

Note- this quartet adds this verse at the end:

Amen Amen Amen
Amen Amen Amen
Amen

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http://www.youtube.com/watch?v=nuF6GMKf17U

Bless the Lord Oh My Soul-New Hope Mass Choir/Bishop Scott

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http://www.youtube.com/watch?v=hb1W1J0zlKw&feature=related

Judith McAllister "Bless The lord, O My Soul"