You didn't indicate how much you would like to pay, so this answer is general. I owned an E32 1989 735iL and now have a 1996 E38 750iL. The E32 had more problems than the average car guy would ever want to put up with. Electronics were new in 1988 and not very good. They caused a lot of problems 7 or 8 years later. I had the car 4 years and spent several thousand dollars to fix things.
My E38 on the other hand has been excellent. None of the electronic gremlins of the E32, no transmission problems, no suspension problems, no a/c rebuilds. In fact it's sort of dull. Until you get on the road!
As mentioned, take care buying a used 740 V8 from '94 through '95 or so (don't remember the inclusive dates). A Nikasil engine could leave you with a virtually worthless automobile.
If you're considering an E23 7, they are not as complicated but are old enough to need a lot of work, depending on how they have been maintained.
Quick reference for 7 cars:
E23 -- through 1987
E32 -- 1988 through 1994
E38 -- 1995 through 2001
And I assume you don't want one of the horrid E65s or E66s.