Prodive are a huge chain with a good international reputation. I can't recommend them directly because I didn't go there but I do know people who did their IDCs with prodive Florida and spoke highly of them.
Supershark mentioned Thailand - this is often an option for those with a more limited budget. Living costs are so cheap there that the cost of internship + flights + living can be far, far cheaper than attending a school in US or Europe.
As an SSI rescue diver you should be eligible to enter the PADI divemaster program straight away (assuming all other requirements are met); once this is completed and you have the required 100 dives you may attend an IDC and IE. For the professional ratings, these are the two courses you need to complete (also an Enriched Air Nitrox Specialty course is verrrrrry useful, you can't teach this without it). Everything else that's offered is just trimming - some places will offer gear or extra courses or other temptations but you need to focus on what is core and then have a look at the extras and compare value for money.
Of course - you don't need to be a PADI instructor - you could stay with SSI and become an SSI instrctor - although you'll find that in certain places, SSI don't have as much of a prescence as PADI.
Write to the schools you are interested in attending and ask them how they would approach your training. Consider you may be spending a few months without an income and make sure you can afford living costs if you need to relocate.
I tend to recommend looking at the bigger, 5* CDC centres. Some people will disagree and suggest a more intimate training environment rather than the so called "instructor factories". Again, speaking from experience I would suggest if you're going to be spending some time away from home, a big school with a lot of students is a cool place to be and hang out and make friends, bounce ideas and learn from each other. During an IDC especially, big class size does not interfere with your training - most of the big schools (if not all of them) will divide the course into groups appropriate to the local Instructor Exams. I used to work at a big school in Thailand (same as scubashark as it happens) and I think we can both safely say we had an absolute blast there!
Good times!
Smaller schools often do not have full time staff cabable of training instructors. This is not always a problem but it means that IDCs can be limited in terms of when they occur. If you'd rather attend a smaller school get word-of-mouth information from former students and dig a little deeper. Again - no disrepect for the smaller shops but it is difficult to compete in the market so make sure you know exactly what you'll be getting. I know of shops that offer IDCs but are actually effectively acting as 'booking agents' for an IDC where a number of smaller shops combine forces with a local Course Director. Again, not necessarily a bad thing, just something to consider.
Hope that helps - good luck!
Crowley