Definitely check out "Rainbow Rising", and "Long Live Rock n Roll", with RJD on vocals. And for Joe Lynn Turner era Rainbow, you might want to check out "Finyl Vinyl"...you can get it on CD, but its a release that has a bunch of hits with Joe on vocals, but some are live, and some are studio. So its pretty cool, too.
Everything starts with "Rainbow Rising" ...it is clearly THE Rainbow album.
You can't over look their first album. Not as flashy or epic as Rising...but an incredible album.
Love Live Rock n Roll is another great album.
Difficult to Cure and Straight Between the Eyes are great for the Turner era stuff.
If you really want to hear Rainbow as its best, get any of the the live recordings from Europe in 1976/1977. POWER POWER POWER!
By the way...do NOT forget about the ELF recordings. If you like Purple, you will enjoy these!
Ah, yes...I agree with Peter...I forgot about that 1st album that came out before "Rising". It is very good also...cool art work on the cover, I think, as well...just like "Rising".