I agree with kthan. A strobe is really necessary if you want better than average pictures. I shot without a strobe for around 3 to 4 trips. Finally I get a chance to shoot with a strobe and the difference is amazing.
It is a good investment and if you are willing to pay a bit more, they can go along with your equipment upgrade.
You should consider these strobes.
Inon D180/s or D2000:
Optically triggered and can be used on almost all consumer digital cams. Can be used on Nexus DSLR housing if you plan to upgrade.
Ikelite DS50, DS125, Inon Z220/s & Sea and Sea YS-90DX
The ikelites can be optically triggered by a manual slave sensor and by a sync cord. No problem with upgrading to DSLR.
Inon Z220/s and Sea and Sea can also be optically triggered triggered by a fibre-optic or a sync cord
If you are really thinking of upgrading next time to a DSLR, I would advise choosing one from the 2nd group. If you just want to upgrade from one consumer digicam to the next, any strobe listed above would do.
For more information, refer to the link below
http://www.digitaldiver.net/strobes.php
A strobe is a good investment