ForecaWeather is very good for me, and also the standard media player widget, which is a little buggy.

If you use a cellular data connection, you will like the Personal Dataplan Monitor widget.

If you use a lot of different networks and you're doing some networking thing, then the Personal IP Address widget is just for you.

If you like the FM transmitter, there is a Simple FM Transmitter widget, too, which lets you quickly enable/disable it and jump into its settings quickly.

If your network operator uses USSD codes (eg. *102#), there is a USSD widget for that.

If you like to see lyrics when you play music, there is a TuneWiki widget. (Downloadable from Ovi Store.)

If you'd like to record your phone conversation, use recaller.

There are multiple widgets which do slideshows or photo displays.

There are also Facebook and Twitter (called Mauku) widgets.

If you like to see how much time is remaining till some events, the Countdown widget is for you.

I think it is a fairly large list, pick the ones you like.