Start off at SFC Universe, and follow the links. Read through these forums, and note websites listed by the posters... many or most are accomplished modelers and such and promote downloading and sharing of their fine works. Its overwhelming to try to think of just one to look at- there's just so many!
Besides, although its fun to play with uber-ships, they tend to make dramatic advantages... I turned Atolm's Soulwolf into an uber-ship on my home conquest, and it was all but unstoppable... it and a couple of frigates could take out a starbase and all its escorts in 10 minutes... such 'ridiculous' firepower makes an unfair advantage in a more than one-player setting.... some persons would abuse that capacity. Not a lecture, just an suggestion.