EGIS wiki space (here)
Tables in text formats can be read directly by ArcGIS. ArcMap and ArcCatalog interpret files with a txt, csv, or asc extension as comma delimited by default. Files that have a .tab extension are interpreted as tab delimited by default.
You can control how the text file is read by editing a the file schema.ini.
ArcGIS can open Excel files directly. Remember: Excel is not a database. You have been warned.
MS Access can easily link data from Excel spreadsheets, which allows a bit of the best of both worlds.
For more information, and a warning:
Although it appears to work most of the time, and seems very convenient, ESRI does not recommend opening access .mdb files in both ArcGIS and Access... it's best to use .mdb format files for one, or the other.
Why? ArcGIS thinks all .mdb files are personal geodatabases, and will add things like index files that Access will not recognize. The same is true the other way – Access will put files in there that ArcGIS does not expect, or omit files ArcGIS expects, since ArcGIS thinks it's a geodatabase.
ESRI instead recommends accessing Access tables using ODBC (ie creating a data source using Windows). This has an additional benefit – you can open dynamic queries as well as tables. This is important because things like cross tabs or other complex joins are very slow and inefficient in ArcGIS – doing the same operation in Access could be 10x (or 1000x) faster. Access also allows access to much more powerful SQL queries than ArcGIS supports, so you can do things like summary and union queries.
A warning about field naming It is best to stick with field names are all caps, start with a letter, under 10 characters, all alphanumeric except "_". If you follow this advice you are much less likely to see your field names corrupted when moving a table from one data format to another, for example, geodatabase tables to .dbf. See Setting up Anaconda open-source Python with ArcGIS.