Here's my $0.02:
What are your favorite lever action guns?-
I like the Winchester Model 88 in .308 and I consider it to be the best lever there's ever been. But I'll admit I'm a Winchester guy. I also like the Winchester 1894s a lot. Many people feel the Marlins are a better value, and they come in some very intelligent caliber/barrel combos. Browning makes the BLR which is kind of ugly and expensive IMHO but you can't beat Browning's workmanship. And you can get it in 7mm magnum.
How effective do you think they could be in a combat situation?- If you mean like home defense, I guess they're as good as any other sporting rifle, probably better than a bolt action. If you mean a social upheaval senario where you're defending your property and family against hordes of evildoers, I think a military type rifle would be better (AR-15, FN-FAL, AK-47).
What specific lever rifle- handgun combos do you prefer,and in which caliber.-
I don't really have a rifle-pistol combo but if you want to share a common cartidge between your rifle and pistol, I would submit that the .44 magnum is the way to go.
Do any manufacturers make high quality black synthetic light
weight models?-
Winchester makes a couple of synthetic stock '94s. You can buy aftermarket synthetic stocks for Winchesters and Marlins through Cabela's and Red Head. If you haven't done so, you may want to check the websites for current production model rifles (www.winchester-guns.com, www.marlinfirearms.com, www.browning.com) and some of the online auctions (www.gunsamerica.com, www.gunbroker.com) for out-of-production models.
Hope this helps. Good luck.