Most airlines arrive at main Vilnius international airport (http://www.vilnius-airpor...) and smaller seaside Palanga airport (http://www.palanga-airpor...), while no-frills carriers Ryanair land in Kaunas international airport (http://www.kaunasair.lt/i...) Kaunas airport also has direct link with [Riga] with AirBaltic.
Majority of flights are operated by Ryanair (http://www.ryanair.com/).
For destinations in Northern Lithuania Riga airport is an attractive option.
While the main railway connecting Lithuania and Poland is now crossing a piece of Belarus which cannot be entered without a visa by most, there is fortunately a minor line left that connects the two countries directly. The border stations are Šeštokai Lithuania and Suwałki Poland. There are only a few passenger connections a day and you need to change trains at the border, because of the different rail gauge used in the two countries.
A popular alternative of crossing the border, if you are going on a longer distance, is to use the bus between Vilnius and Warsaw.
Major "Via Baltica" road links Kaunas to Warsaw and Riga/Tallinn. The Baltic road, which links Vilnius to Tallinn, was just reconstructed. It is a very easy and pleasant route.Overall, the major roads between the cities are of decent quality. Be extremely cautious when getting off the main roads in rural areas, as some of them may contain pot holes and general blemishes which could damage a regular car if you go too fast.While driving between cities there are usually cafes and gas stations with bathrooms and snacks.