I think that, if you are able to import your html tables in Excel or OpenOffice Calc, these tools are what you need:

• 
  Excel2LaTeX for MSExcel


• 
  Calc2LaTeX for OO Calc (this one is my preferred, guess why ;)

The first one is a macro you add to your Excel, and provides you with an extra button to create the LaTeX code for the table from a set of selected cells, ready to be pasted in your .tex source.
The second, is an extension of OO, but should work in the same way.

Edit: there is also html2LaTeX, but I never used it.

Happy TeXing!

Check out this page http://www.ctan.org/tex-archive/help/Catalogue/entries/datatool.html and tools it links ie csvtools and pgfplotstable. They allow you to keep the data in csv or tsv format and configure typesetting options in .tex source. I have used pgfplotstable and it is very handy.

The on-line LaTeX table editor at http://truben.no/latex/table/ is very handy. You can import your data in LaTeX, JSON or CSV format (the last of these being relevant to this question), and export it in LaTeX format (among numerous other formats). It's also very easy to insert/delete columns, etc., and change the formatting.

you can try this one: http://www.tablesgenerator.com/latex_tables#

it can generate latex table codes as well as other formats like markdown, html, wiki etc.

If you use TeXShop on the Mac, there is a built-in macro for pasting copied spreadsheet cells directly into your latex sources into a variety of popular table formats. The same scripts are also available for other Mac text editors here: csv2latex. (OB Disclaimer: I am the author.)

CALS tables

Perhaps you will feel more comfortable defining tables in CALS syntax immediately in LaTeX.

The CALS table model is the historic precursor of the HTML table model. It is easier in use and offers more capabilities than tabularx.

Here is the documentation of the cals package:

• 
  http://www.ctan.org/tex-archive/macros/latex/contrib/cals (demo & doc)


• 
  http://tug.org/TUGboat/tb32-2/tb101parashchenko.pdf (user's manual)

As long as you can transform the table you want to import to one of the formats that Python pandas module reads or you can read it in in Python and use tabulate module to output the properly LaTeX-formatted table which could be a good starting point.

• Recipes from this StackOverflow question can be a good starting point if you do not know Python

Calc2LaTeX is the best option as said above, but if you're constantly switching computers or on a mac (I regularly do both), then an online editor is a good option.

I have found http://www.tablesgenerator.com/latex_tables# is the best online editor, as efinal recommended, because it also converts & % to & % straightforwardly, which http://truben.no/latex/table/ doesn't, as far as I can tell. The Truben Table Editor was no good to me as the paste command simply pasted an entire table into one cell, fustratingly.

If you use TexStudio, there is a wizard for tabular, looks like