I concur with richardtallent. The big name database systems have all provided us with good tools for large databases. (2 million rows is nothing, although you can see performance issues with lousy indexes or poor choices in the select statements, especially if you are joining across multiple tables of similar size.). It comes down to pros and cons with costs, usability, cost of support, etc.
I can speak most to Oracle and SQL Server. Oracle is pretty pricey, and it takes a pricey, dedicated DBA to really use it right. It isn't known for usability, but a DBA or programmer comfortable with it can work just fine in it. It also has great flexibility and some believe it is more powerful than the others. (I don't know if that's true or not, but I know it certainly provides lots of different ways you can tweak it for efficiency, etc.)
SQL Server can certainly handle large datasets just fine. It has a "prettier" face and tends to be considered more usable, but usability in the end is a matter of opinion. It does have a cheaper price tag, but you might have just a bit less flexibility than Oracle. You can get a "cheap" SQL Server dba, because its user-friendly interface makes it easy for people to do some of the basic DBA tasks without being experts. But you get what you pay for (usually) and if you really want efficiency and security, you pay for an expert anyway.
Those are just a few of the things to consider when looking at DBs. I'm sure MySQL and DB2 have their own pros and cons to be weighed.
But none of them have a problem with a measly 2 million rows. (I regularly work in a database with hundreds of tables, some of which have over 50 million rows, and I see little performance hit b/c the DBAs know what they are doing.)
FOLLOW UP EDIT: Since this is for a website, maybe your biggest consideration should be integration of front/back. For example, if you are using ASP for the web, SQL Server is a natural choice.