Ryanair and Aer Lingus are the only carriers between Dublin and Birmingham.
East Midlands isn't that far away depending on where exactly you're going and what your ground transport options are .. BMIBaby (www.bmibaby.com) and Ryanair fly there .. BMIBaby are dropping this route at the end of March .. but if you're going before then might be some reasonable deals.
I've flown out of BHX a couple of times and I'd be wary of getting the last Ryanair flight. Often, 'your' plane picks up late minutes throughout the day and, by late evening, there's no way it'll get to BHX in time. So they have to get a plane from somewhere else, i.e., you'll be there until 10-11pm!!
Having said that, Ryanair claim to be one of the most punctual airlines in Europe (& I'm a fan). Maybe it's specific to Birmingham??