First of all a link to Stephen G. Hartke's »A Survey of Free Math Fonts for TeX and LaTeX« and Walter Schmidt's »Mathematikschriften für LaTeX« (in german).
Many fonts come with math support. If you haven't taken a look at those, do so. They can be found on the page with Fonts with math support.
The euler package provides some math support using the euler fonts.
\usepackage{euler}
or with one or more of the options
\usepackage[mathbf,mathcal,text-hat-accent]{euler}
The eulervm package provides some math support using the euler fonts too, but uses some enhanced virtual fonts.
\usepackage{eulervm}
or with one or more of the options
\usepackage[small,text-hat-accent,euler-digits,icomma,OT1,T1,LY1]{eulervm}
The sansmath package provides some math support for sans serif fonts.
\usepackage{sansmath}
\sansmath
or with one of the options
\usepackage[eulergreek,EULERGREEK]{sansmath}
\sansmath
The sfmath package also provides some math support for sans serif fonts.
\usepackage{sfmath}
The sfmath package has a wide range of options. View the package source for details.
The sfmath package has an supporting package in the sansmathaccent package which corrects the placement of accents.
\usepackage{sfmath}
\usepackage{sansmathaccent}
Another way of generic math support is the package mathastext.
\usepackage{mathastext}
This will make your document use the main text font also in mathematics mode. The default is that the letters in text and math mode have the same shape but option `italic' will make the letters use the italic shape in math mode. Digits and log-like operator names will be upright (if the text font is upright). So one can now typeset documents (containing simple mathematics formulas) with a quite arbitrary TeX text font, without worrying too much that nobody ever designed accompanying math fonts.
View the full package information at http://tug.ctan.org/pkg/mathastext/.
The MnSymbol package provides math support for the Adobe MinionPro fonts, but may also work with other fonts. The MnSymbol package is part of TeX Live. It can be found on CTAN at http://www.ctan.org/info?id=mnsymbol.
\usepackage{MnSymbol}
or with one of the options
\usepackage[mnsy,cmsy,abx]{MnSymbol}