Excel Add-In

ad Science: StatEL
Excel addin for non-professional users of statistics. Helps the user to conduct a proper analysis and to understand the results. Works on Windows and MAC OS X. Free demo available.
http://www.adscience.eu

Analyse-It
Statistical software integrated into Microsoft Excel for linear regression, anova, chi-square and other functions. Download evaluation.
http://www.analyse-it.com/

ConnectCode: TinyGraphs
Open source Excel add-in that creates sparklines charts and graphs.
http://www.spreadsheetml.com/products.html

EZAnalyze
Free Excel Add In designed to permit the calculation of basic descriptive and inferential statistics without selecting ranges or typing formulas
http://www.ezanalyze.com

Microsoft Data Analysis Toolpak
Free add in included with Excel but not enabled by default. Calculates many descriptive and inferential statistics.
http://office.microsoft.com/en-us/assistance/HP052038731033.aspx

QETools
Six Sigma statistical tools (Excel Add-in) from basic descriptive statistics and hypothesis testing to control charting, regression, and ANOVA. Demo download. Purchase online.
http://www.qetools.com

SigmaXL
SigmaXL is an add-in for Microsoft Excel 2000 and higher. It enables the user to measure, analyze, improve and control their service, transactional and manufacturing processes. Free demo is available.
http://www.sigmaxl.com/

statistiXL
Statistics add-in for Microsoft Excel. Includes univariate and multivariate tests such as ANOVA, Correlation, Regression, PCA, Factor and Discriminant Analysis.
http://www.statistixl.com

StatTools
Advanced statistical analysis add-in for Microsoft Excel. StatTools replaces Excel's statistics function with 36 robust statistical procedures.
http://www.palisade.com/stattools/

Unistat Ltd.
Makes and sells Unistat for Windows: comprehensive stand-alone statistical package that can also be an Excel add-in. A one stop solution for data handling, analysis, and presentation quality scientific graphics.
http://www.unistat.com/

WinSTAT
An Excel Add-In providing statistical tests and diagrams. Demonstration download.
http://www.winstat.com/

XLMiner
XLMiner is a comprehensive data mining add-in for Excel, with neural nets, classification and regression trees, logistic regression, linear regression, clustering, and principal components. Trial version available, requires Excel 2000 or later.
http://www.resample.com/xlminer/index.shtml

XLSTAT
Data analysis and statistics add-in for Excel. Includes over 40 statistical and data analysis features for statistics experts, researchers, students, and teachers. Buy on-line or download trial version.
http://www.xlstat.com/

Zumastat
Provides ability to calculate confidence intervals for correlations, power analysis, and meta analysis (and many more) using summary statistics. Contains many advanced functions. Evaluation download not available, purchase online.
http://www.zumastat.com