Ok, so most places in SL don't have much to see underwater, but some do and it's just corny to be flying everywhere, especially underwater and especially if you're trying to role play. Therefore, you need an affordable but stylish, steampunk submarine. The Steamsquid is an easy to drive, but fairly realistic-ish steam powered submarine of the steampunk, physical vehicle variety. Medium sized, there is room for two passengers in addition to the pilot. Plus, it's cheap, but only because I made it for myself and I'm not greedy.
Quite simply, this is my favourite starter submersible! VERY easy to handle, and unparalleled field of view. Unarmed, but this is an observation craft, not a warship - people who cruise in glass submersibles shouldn't fire torpedoes!
My only quibble is with her tendency to automatically submerge when traveling, without the helmsman ordering a dive. Keeping her cruising on the surface is somewhat annoying. If she had neutral bouyancy, and only surfaced or dove on command, this would be the perfect maritime observation craft.
Still worth 5 stars, though, even with this quirk. At the price, there is simply nothing finer in her class.