NOTE: Most names need to be entered in Lithuanian form, especially those for which you might have the Polish version. For example, the Polish ending -iewicz will usually require Lithuanian -evičius (without diacritical marks typically accepted). Furthermore, Lithuanian has inflectional endings for female surnames that indicate if married or unmarried. It is complicated. Some sites are helpful with close matches shown as you type from which you can choose.
General & National
Church Records – Metrical records from many areas across Lithuania
Cemeteries – Search multiple cemeteries by surname, year of death; usually includes a photo of the headstone (in Lithuanian, but enter surname to search)
Cemeteries – Search multiple cemeteries by surname; usually includes a photo of the headstone (in Lithuanian, but enter surname to search)
Cities & Villages
JewishGen – Lithuania Collection – Premier international Jewish genealogy website