i actually own all these + many more of my old vinyl collection on digital master also, thanks to the large selection of unmixed german compilation albums that came out in the 90's, not to mention a suprising amount of cd single releases of tracks that were and still are rare as white dog poo over here (see si the sighs thread for more info on white dog poo)
There have been all kinds of obscure ones aswell as some easier to obtain ones over the years.
a great place to start is the trancemaster series, not the new ones because there garbage but volumes 20,21,22 are the strongest of the series, full of late 90's classics. also various world of trance compilations from around vol 10 up have a lot of the classics scattered around the series.
The early dream dance compilations have some good stuff but most of it are radio edits of around 3-4 mins which is fine for listening but not so good if you intend to mix the tracks.
i will go through my cd collection in the week and make a list of the compilations i think are the strongest and post it here, you will most likely be able to find people with most of them for sale via discogs.