Optima's web site is out of date now. They do have one that will drop in an Insight, civic, S2000 etc. It's a group 51 size battery. They make two so make sure you get the right one. You'd want SC51DA, there is another just like it, but the posts would be positioned incorrectly so make sure you find the correct one. There are a few people on the yahoo group who have bought them for their Insight's recently.
Now that thats said I'll try to talk you out of it. Optima's are bloody expensive for what you get. I think the particular battery I'm talking about is about $120 or so! Probably more if you go buy it locally. And from personal experience optima's are way over-hyped. I had one in my last truck, shelled out $140 for the deep cycle one. They are apparently supposed to last twice as long as conventional batteries. Most of the time I just used it to start the truck, occasionally I let it power the stereo while say at the lake or something, but it never got drained as deeply as your supposed to be able to take them. Well less than two years later the thing was nothing more than a oversided paper weight. I was needless to say very dissapointed.
My personal recommendation, if you don't need much standby power for running a stereo or something I'd suggest going the other way with a small Hawker battery like I did: http://www.insightcentral.net/forum/viewtopic.php?t=529
There are larger ones too, I haven't found any bad reviews for hawkers. The little things are rated for 400 cycles to 100% discharged! I've had the one in my car for about 7 months now and it's been just fine. I've been monitoring it for any decrease in voltage, but none so far. You can pick up a little 13 ah one like I have for around $30 too.