My embarrassingly large stock of unbuilt kits includes a nice resin 1/350 German U-boat from Bluewater Navy. I believe that firm is now defunct, but its kits seem to be surfacing occasionally under other labels. I think I bought it from Model Expo; maybe they still have access to it.
For a long time the available plastic WWI ship kits available (if you don't count the Airfix Mauretania) could almost be counted on one hand. Revell and Airfix did 4-stack American destroyers, and in the '70s Airfix produced a pretty good HMS Iron Duke (which is still available, I believe). Revell also sold a kit that pretended to represent the German WWI raider Seeadler, but it was a slightly modified reissue of the firm's USCGC Eagle. And ITC had a US Navy subchaser (subsequently reissued by Glencoe). Things are a little better now, but not much. We have the 1/350 German battleships from ICM (nice kits as I understand it, though I haven't bought them). And there are some beautiful resin kits from firms like WSW and White Ensign - expensive, but with the potential to produce pretty spectacular results. If you're interested, a good place to get acquainted with them is the Steel Navy website: <www.steelnavy.com>.
It's a shame the period hasn't been covered more thoroughly by kit manufacturers. It's a crucial one; it could be argued that warship technology exerted a greater influence on world events between 1890 and 1918 than in any other period in history.
Good luck.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.