I've always liked the idea of exploring the moon Titan, most likely because of the atmosphere, pressure, and the fact that it has stable bodies of liquids at the surface. Although it's very cold, these factors may increase the chance of life being there. So, does anyone know if and when we will send another probe (most likely unmanned) to Titan? Are there any missions planned within the near future?
A colleague worked on the Titan Mare Explorer (the concept did not proceed beyond proposal stage). It was an ultra-cool idea that would include to lower a boat to sail the seas of Titan (doesn't that sound catchy?). Alas, it wasn't selected; instead, NASA selected the InSight Mars lander — NASA keep changing their priorities as to where they want to go.
There are currently no active plans to return to the Saturn system. Personally, I believe that the next landing in the outer solar system will not be on Titan, but on another moon, such as Europa or Enceladus. But it will be a bit down the road; neither upcoming JUICE (ESA Jupiter mission), nor Juno (NASA Jupiter mission) include any landers.
NASA's currently planned and funded (to some extent) future missions are listed here: http://www.nasa.gov/missions/future/. Alas, nothing is currently planned for Titan.
I guess other agencies/organizations might have something.
The Phys.org article Researcher sets eyes on Saturn's largest moon describes the Dragonfly project; the potential application of large (~2 meter) quadcopters on Saturn's moon Titan.
Dragonfly is one of two NASA recently short-listed– from an original proposal group of a dozen – as part of the agency's New Frontiers planetary science program.
An artist’s rendering shows the proposed Dragonfly quadcopter landing on the surface of Saturn’s moon Titan, unfolding its rotors and lifting off again to survey the landscape and atmosphere. Credit: Steve Gribben/Johns Hopkins APL
Dragonfly was one of two mission concepts down-selected for the next New Frontiers mission at the end of 2017. The other is a comet sample return. One of those two will be selected in July of 2019.
Even if Dragonfly is not selected, it is very likely that the "Ocean Worlds" objective will remain for the subsequent New Frontiers call, which would be satisfied with either a Titan or Enceladus surface exploration. The other objectives are a Lunar Aitken Basin Sample Return (though it looks like China may be planning to do that soon), a Saturn Atmosphere Probe, a Jupiter Trojan Tour and Rendezvous, and a Venus In Situ Explorer. Generally New Frontiers objectives remain until satisfied with a mission. Previous New Frontiers missions are New Horizons, Juno, and OSIRIS-REx.
The boat mentioned by gerrit reminded of another concept. The idea is to put a blimp into Titan's atmosphere and fly around.
Colombatti, G., La Gloria, N., Aboudan, A., Debei, S., 2009. Airship's Dynamics Modeling and Control Strategy for Titan exploration. Proceedings of the 60th International Astronautical Congress - IAC-09.A3.I.12.
In terms of background for your question: There are certainly plenty of types of missions investigated right now. Unfortunately, the chances of such a mission actually receiving the required funding are slim. So the result is a wealth of good ideas, some even developed in very high detail, but virtually non of them fly. My habit is to "ignore" them unless they turn up in high level agency documents and political discussions. Otherwise it is just too painful to see them catching dust over time. From this point of view, there are no missions as of today planed for another visit of Titan.