The TIS is what the dealerships use; it far and away surpasses the Bentley manual for completeness on any given model.
The ETK (parts catalog) is useful, but virtually the same as realoem.com. I prefer the Penske site, as I can search for parts (and up to date pricing) more easily.
The ETM (electrical troubleshooting manual) is invaluable if you need to trace a single wire. Consider that the ETM of my 01 comprises over 400 pages, nearly what the Bentley devotes to the entire car, so how complete is Bentley's wiring diagrams?
The KSD (flat-rate manual) is useful for quoting how long a given job should take, if it's something you haven't done before. It's "unit" of measure is seven (7) minutes; take the number of units per task and multiply by 7 for total time.
Those are the most useful CDs of the routinely available sets found on Ebay, and practically any issue date with have the complete data for these "old" cars (the first 1.9s now being seventeen__17!__years old...). Given that whole sets are available for $15-20 (and they're far-far more complete) it amazes me that Bentley can sell their books, but yes, I have one too...
1957 Austin-Healey 100/6 Wine Red
1961 McCulloch R1 go-kart Screaming Yellow
1995///M3 Coupe Dakar Yellow Eurosport Twinscrew S/C
1999///M Rdstr Cosmos Black Eurosport Twinscrew S/C
1999///M Coupe Estoril Blue Eurosport Twinscrew S/C
2001///M Rdstr Steel Gray
2011 X5 35i Sport Deep Sea Blue/Cinnamon