Inspired by Andrew Stacey's pretty drawing, here's a take on two of the pictures you linked to. Once you start with drawing stuff like this, you'll pretty quickly accumulate your own library of elements, and every successive drawing will be easier.
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc,patterns,decorations.pathmorphing,decorations.markings}
\begin{document}
\begin{tikzpicture}[every node/.style={draw,outer sep=0pt,thick}]
\tikzstyle{spring}=[thick,decorate,decoration={zigzag,pre length=0.3cm,post length=0.3cm,segment length=6}]
\tikzstyle{damper}=[thick,decoration={markings,
mark connection node=dmp,
mark=at position 0.5 with
{
\node (dmp) [thick,inner sep=0pt,transform shape,rotate=-90,minimum width=15pt,minimum height=3pt,draw=none] {};
\draw [thick] ($(dmp.north east)+(2pt,0)$) -- (dmp.south east) -- (dmp.south west) -- ($(dmp.north west)+(2pt,0)$);
\draw [thick] ($(dmp.north)+(0,-5pt)$) -- ($(dmp.north)+(0,5pt)$);
}
}, decorate]
\tikzstyle{ground}=[fill,pattern=north east lines,draw=none,minimum width=0.75cm,minimum height=0.3cm]
\node (M) [minimum width=3.5cm,minimum height=2cm] {mass, $m$};
\node (ground1) at (M.south) [ground,yshift=-1.5cm,xshift=-1.25cm,anchor=north] {};
\draw (ground1.north west) -- (ground1.north east);
\draw [spring] (ground1.north) -- ($(M.south east)!(ground1.north)!(M.south west)$);
\node (ground2) at (M.south) [ground,yshift=-1.5cm,anchor=north] {};
\draw (ground2.north west) -- (ground2.north east);
\draw [damper] (ground2.north) -- ($(M.south east)!(ground2.north)!(M.south west)$);
\node (ground3) at (M.south) [ground,yshift=-1.5cm,xshift=1.25cm,anchor=north] {};
\draw (ground3.north west) -- (ground3.north east);
\draw [spring] (ground3.north) -- ($(M.south east)!(ground3.north)!(M.south west)$);
\draw [-latex,ultra thick] (M.north) ++(0,0.2cm) -- +(0,1cm);
\begin{scope}[xshift=7cm]
\node (M) [minimum width=1cm, minimum height=2.5cm] {$m$};
\node (ground) [ground,anchor=north,yshift=-0.25cm,minimum width=1.5cm] at (M.south) {};
\draw (ground.north east) -- (ground.north west);
\draw [thick] (M.south west) ++ (0.2cm,-0.125cm) circle (0.125cm) (M.south east) ++ (-0.2cm,-0.125cm) circle (0.125cm);
\node (wall) [ground, rotate=-90, minimum width=3cm,yshift=-3cm] {};
\draw (wall.north east) -- (wall.north west);
\draw [spring] (wall.170) -- ($(M.north west)!(wall.170)!(M.south west)$);
\draw [damper] (wall.10) -- ($(M.north west)!(wall.10)!(M.south west)$);
\draw [-latex,ultra thick] (M.east) ++ (0.2cm,0) -- +(1cm,0);
\end{scope}
\end{tikzpicture}
\end{document}
You should use the siunitx package to format all your numbers and units.
The symbol can be drawn using \diameter from the wasysym package and the tolerances are simple math super- and subscripts:
\documentclass{article}
\usepackage{wasysym}
\usepackage{siunitx}
\sisetup{output-decimal-marker={,}}
\newcommand{\tol}[3]{\ensuremath{\si{#1}^{+\num{#2}}_{-\num{#3}}}}
\newcommand{\diatol}[3]{\ensuremath{\diameter\si{#1}^{+\num{#2}}_{-\num{#3}}}}
\begin{document}
\diatol{0,125}{0.000}{0.001}
\tol{2,225\meter}{0.100}{0.20}
\tol{2,225m}{0.100}{0.20}
\end{document}
Result:
Best Answer
I suggest you mix-and-match.
For truly arbitrary yet still technical drawings (even complex ones) like parts of an aircraft and mechanical components, I would suggest Google SketchUp. As a taste of drawing a model jet, consider viewing a quick YouTube video.
You can also use parts of already-created models from the 3D Warehouse:
You can even scale up to full size:
As a tutorial on working with SketchUp, consider the Harwood Podcast Network SketchUp: A 3D Toolbox podcast. Also see Draw an aircraft with Tikz.
For mathematical graphs and diagrams (something that has more expressible structure, mathematically), you can use any of the graphical packages used throughout this site:
tikz,pstricks, Asymptote, ...