First of all, there is no single or unique ‘Garamond’ font as such, but for the historical fonts cut by Claude Garamont (1499-1561). However, there is a whole bunch of Garamond-looking fonts, some based on the work of Jean Jannon (1580-1658).
That said, the mathdesign package allows for typing both maths and text with URW Garamond N°8: just add to your preamble:
\usepackage[garamond]{mathdesign} or \usepackage{ugm}
It can be complemented with the garamondx package, which adds true smallcaps, oldstyle figures and the f-ligatures to the ugm set of fonts.
The newtxmath package has a garamondx option to use the math italics part of the garamondx package.
Another beautiful font available for (pdf)LaTeX, XeLaTeX, LuaLaTeX is ebgaramond, redesigned from a historical specimen that shows a Garamont roman font and a Jannon italic font at different sizes. It exists in Opentype and Type 1 formats, but it has no bold version for the moment (hence a cheaper printing!). It has been complemented a few days ago by an ebgaramond-maths package that works with newtxmath.
\usepackage{xcolor}\color{white}in the preamble also saves much ink ;^) – Steven B. Segletes Apr 03 '14 at 13:05\usepackage{garamondx}as indicated in a comment at http://tex.stackexchange.com/questions/150628/monotype-garamond – Steven B. Segletes Apr 03 '14 at 13:09ebgaramondpackage, as mentioned in the accepted answer at http://tex.stackexchange.com/questions/60098/eb-garamond-on-latex. See http://www.ctan.org/tex-archive/fonts/ebgaramond – Steven B. Segletes Apr 03 '14 at 13:15\usepackage[garamond]{mathdesign}allows using URW Garamond No8 for maths (and text of course). – Bernard Apr 03 '14 at 13:30\usepackage[light]{kpfonts}. – Speravir Apr 04 '14 at 00:15