I'd strongly recommend shortcutd - it allows you to control the device in more ways to your taste.

On the games front I only use EightyOne (for sudoko) and unnethack.

If you use the FM transmitter, the combination of FMRDSNofify and the stock media player widget is quite good. On the other hand I think Nicolai's Calendar Home widget is much better than the stock Maemo one. I've also installed his Scout device search app, but not used it much.

I have OMWeather installed as I like it's customisability.

If you want to do much hacking, you'll need a text editor; I like PYGTKEditor, which has syntax colour coding. I also like Quicknote for, er, taking notes quickly...

If podcasts are your bag, the gPodder/Panucci combo's pretty hot.

As for tips, have a look at the wikilinks in my sig.