Well, in my opinion, some kits that don't look too exciting but are clean-looking are a number of Tsunami front lips. I'm not sure if the stock front bumpers of 98 Civics are the same as the 99-00 ones (I'm sure someone knows around here) but the Tsunami T1 looks really nice. I question the differences between the 98 and 99-00 front bumpers because the T1 goes real well with the 99-00 front bumper. As for the rear bumpers, I'd go with the Buddy Club rear or Black Widow, as others have said already. For the sideskirts, I'm not really sure, but the Buddy Club ss look tiiiiite. Hope that kinda helps.
I'm thinking of a less aggressive look for my ride too, AFTER I make my performance mods, of course. My setup would be something like the T1 front lip, stock ss(I'll just make them the same color as the rest of my ride), and maybe the Buddy Club rear(which will most likely hang lower than the ss so I'll see about the rear). Anyways, that's just extra info I wanted to share regarding my plans. Lates!