Question: I would like to combine, somehow, `\vec{x}` and `\dot{x}` so that I get an x with a vector arrow over it and a dot over that. Any suggestions?

Answer: 
How about the obvious, i.e. `$\dot{\vec{a}}$`? Spacing is a little off... which could be fixed by using the [`esvect`](http://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CDEQFjAA&url=ftp://ftp.dante.de/tex-archive/macros/latex/contrib/esvect/esvect.pdf&ei=hDIIUZa4DMjitQbB24CQBQ&usg=AFQjCNHzfqiWohF7Fk367TOodXEL_Luklg&sig2=JekK-1CsoUpsB2RFZ3nGHw&bvm=bv.41524429,d.Yms) package (for vectors in general) and using: 

```tex
\documentclass{minimal}

\usepackage{esvect}

\begin{document}
$\dot{\vv{a}}$
\end{document}  

```

Result using first solution is on left hand side, using `esvect` is on right hand side: 

![result](https://i.stack.imgur.com/NMow9.png)

---

**UPDATE:**  

I added a little solution of my own which has good spacing *and* uses the normal `latex` vector arrow [but requires the `accents` package]. This can be obtained using the command `\DotVec` (no need for an additional `\vec`; code: 

```tex
\usepackage{accents}
\newcommand*{\DotVec}[1]{%
  \accentset{\mbox{\hspace{0.25ex}.}}{\ensuremath{\vec{#1}}}}  

```

I created a document for comparing my solution, the "plain" `latex` solution and @Eddy\_Em's [I hope that's okay?] solution. Code is: 

```tex
\documentclass{minimal}

%% solution using esvect
\usepackage{esvect}

%% required for looping all letters
\usepackage{pgffor}

%% my solution using the accents package
\usepackage{accents}
\newcommand*{\DotVec}[1]{%
  \accentset{\mbox{\hspace{0.25ex}.}}{\ensuremath{\vec{#1}}}}

%% this is Eddy_Em's solution
\newsavebox{\hght}
\def\dotvec#1{\savebox{\hght}{$\vec{#1}$}\dot{\raisebox{0pt}[.8\ht\hght]{$\vec{#1}$}}}

%% this is used for a little extra vertical space in the below listing
\def\vSpacer{\vrule height 15pt width 0pt}

\begin{document}
\noindent
Order is:
\begin{verbatim*}
\dot{\vec{a}} \dot{\vv{a}} \dotvec{a} \DotVec{a}
\end{verbatim*}
For roman alphabet:\\[5pt]

\par\noindent
\foreach \l in {a,...,z} {%
    \vSpacer $\dot{\vec{\l}} \; \dot{\vv{\l}} \; \dotvec{\l} \; \DotVec{\l},\quad$
}

\par\noindent
\foreach \l in {A,...,Z} {%
    \vSpacer $\dot{\vec{\l}} \; \dot{\vv{\l}} \; \dotvec{\l} \; \DotVec{\l},\quad$
}

\end{document}  

```

Resulting document: 

![result](https://i.stack.imgur.com/ulNrU.png) 

Zoom for letter `a`: 

![zoom](https://i.stack.imgur.com/PMjyA.png)
I did it so:

```
\newsavebox{\hght}
\def\dotvec#1{\savebox{\hght}{$\vec{#1}$}\dot{\raisebox{0pt}[.8\ht\hght]{$\vec{#1}$}}}

```

Some explanations:

* `\newsavebox{\boxname}` defines a "saving-box" — a box which can contain anything for some preprocessing (for example every page before output is placed to `\box255`);
* `\savebox{\boxname}{text}` puts `text` into box `\boxname`, we put there our vector;
* then we need to add a dot to it (`\dot`), but to avoid a large space between dot and vector we "reduce" height of our vector by 20% (`\raisebox` not only "raise" its contents but also can change its height and depth).

Here we've used `\savebox` only to measure height of vector, but instead of vector itself in `\raisebox` argument we can write `\usebox{\hght}`. It could be more quickly because latex won't need to process this box again — it will simply use a ready box.