\documentclass[a4paper, oneside, 10pt]{article}
\usepackage[utf8x]{inputenc}
\usepackage[czech]{babel}
\usepackage{multirow}
\usepackage{longtable}
\begin{document}

\begin{longtable}{|l|l|l|}
\hline
\textbf{Heading 1}   &  \textbf{Heading 2}    &  \textbf{Heading 3}  \\ 
\hline 
 Row 1 Col 1\newline aaaa     &  Row 1 Col 2      &  Row 1 Col 3         \\ 
\hline 
 Row 2 Col 1     & \multicolumn{2}{|l|}{ some colspan (note the double pipe) } \\ 
\hline 
 Row 3 Col 1     &  Row 3 Col 2      &  Row 3 Col 3         \\ 
\hline 
\end{longtable}

\begin{longtable}{|l|l|l|}
\hline
  &  \textbf{Heading 1}    &  \textbf{Heading 2}  \\ 
\hline 
 \textbf{Heading 3}    &  Row 1 Col 2      &  Row 1 Col 3         \\ 
\hline 
 \textbf{Heading 4}      & no colspan this time &  \\ 
\hline 
 \textbf{Heading 5}     &  Row 2 Col 2      &  Row 2 Col 3         \\ 
\hline 
\end{longtable}

\begin{longtable}{|l|l|l|}

\hline
 \textbf{Heading 1}  &  \textbf{Heading 2}    &  \textbf{Heading 3}  \\ 
\hline 
 Row 1 Col 1    &  \multirow{3}{*}{ this cell spans vertically }      &  Row 1 Col 3         \\ 
\hline
 Row 2 Col 1      &  & Row 2 Col 3 \\ 
\hline 
 Row 3 Col 1    &        &  Row 2 Col 3         \\ 
\hline 
\end{longtable}
\begin{longtable}{|l|l|l|}

\hline
 \multicolumn{3}{|c|}{\textbf{Table with alignment}}  \\ 
\hline 
 \multicolumn{1}{|r|}{right}   &  \multicolumn{1}{|c|}{center}       &  left        \\ 
\hline
 left      & \multicolumn{1}{|r|}{right} & \multicolumn{1}{|c|}{center} \\ 
\hline 
 xxxxxxxxxxxx    & xxxxxxxxxxxx  &  xxxxxxxxxxxx         \\ 
\hline 
\end{longtable}

\end{document}