[djohn]

Off the top of my head i can think of the Circa Rave, the topps desert shield, 1996 pacific cramers choice, and pinnacle skylines which i like, also the donruss crusade!!!

Some interesting recommendations.
Topps Desert Shield wasn't an insert set but rather was a parallel of the set distributed in packs to the armed forces serving in 1991. While it is a tough set to put together, you have to be extremely careful when buying the higher end cards from that set as there are fakes out there (since you can simply take a normal 1991 Topps card and add the foil logo after, assuming you have a print shop that can add foil, which apparently some counterfeiters seem to be able to do).
The Donruss Crusade set is an extremely tough set to put together and you will spend quite a bit of money on each card, as there are many people who have started that set.
My favorite thing about the 90s inserts are that there are some really fun to look at cards, like Pinnacle Shades and Leaf SlideShow.
Here is my rundown on the top 5 defining insert sets from the 90s:
1) 1991 Donruss Elite Series (these cards defined CHASE cards, and even though there are 10,000 of each they were still case hits at best).
2) 1992 Topps Gold (this was the first full parallel set inserted into packs and really started the craze regarding parallels)
3) 1993 Finest Refractors (a year after Topps Gold debuted, this parallel set became all the rage and a million refractors later people still love the refractor technology).
4) 1997 Flair Legacy Collection (this was the first set numbered to 100 and the Masterpiece collection parallel were the first 1/1s).
5) 1998 Donruss Crusade (this insert set was the first to cross over between several products: Donruss, Donruss Update, and Leaf. Plus all the parallel colors and serial numbering really made this set hot)