Alternate Greek symbols

\varphi, \varepsilon and so on.

If you want to use one variant throughout and save yourself a few keystrokes, put \let\phi\varphi in your preamble.

The kpfonts package contains slanted and upright greek letters for mathmode.

psgreek provides some alternate Greek fonts.

There are several packages that render slightly different Greek letters, such as the upgreek package.

You can check this and many more in the Comprehensive LaTeX Symbol Guide, starting from page 90.

I came across this document: http://www.tug.org/pracjourn/2006-1/hartke/hartke.pdf, which is a review of different fonts for math mode. In the document it also shows the rendered version of each of the fonts, to give you an impression of what the final result will be like.