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.
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)