The important thing to know before you spend any cash is which strobes are compatible. If I remember correctly, the Sea and Sea YS-01 and 02 strobes only fire via a fibre optic cord, so would not be suitable for your Ikelite housing, and no good for future use with a 5d2.
The same with some of the Inon strobes, the S-2000 and D-2000 cannot be fired by wired strobes.
I'd recommend either looking at Ikelites own strobes or the Inon Z240, or some of the sea and sea strobes that can be used with wired cords such as the D1 or the older YS-110. These will all work with a variety of housings providing you have the correct sync cord.
TTL isn't as popular underwater as it is on land but if you really want it then you'll need to match an Ikelite strobe with y our Ikelite housing. If you go this route, then spending a bit extra to get a DS-125, DS-160 or DS-161 will more than likely prove beneficial in the long term over the DS-51.