The name pretty much says it all. Right now I'm using Squirrel - it crashes frequently and suffers from memory problems (I've tried increasing the heap size). I don't need anything particularly fancy or full-featured - just something that won't take up 2.4 GB of RAM to store a 1.5 million line, 8 column result set.
Try official pgAdmin. http://www.pgadmin.org/download/windows.php
One option would be to use phpPgAdmin on the server. It’s a web app, but it’s lightweight and easy to install.
It can paginate results, so it can handle large result sets. It can’t do everything that pgAdmin can do, but for everyday use I prefer it.
Use PgAdmin.
However - I don't think you'll find much that won't use a large amount of memory when you have a result set with 1.5 million rows...
PgAdmin has the ability to limit automatically the number of rows returned - so you can get an overview, but not sit for an hour waiting for your results to turn up. If you write a query to return that many rows though, than you are going to have problems.
(You can also look at the limit
SQL command, to restrict how many results you get back)
NOTE: This is the same answer I gave this duplicate question.
I haven't tried it yet myself, but others have recommended dbVis. The client runs on Mac, Windows and Linux and supports a variety of database servers, including PostgreSQL.