Once you are a CA, as such you do not need any other qualification. The degree is well-respected and good enough to get a job. However, in this age of extreme competition, doing another degree opens up closed doors and adds value to your CV. Let me tell you what you can do -
1. Finance - What majority CAs wish to get into
a. MBA - The king of all degrees. There is nothing like a CA+MBA. However, having done your CA, I would advise you to do an MBA only from IIM ABCLKI, ISB, FMS, XLRI, SPJain or JBIMS. Advantages are plenty. You might end up getting a top finance job or becoming a management trainee at an MNC. Gives you good alumni base as well as improves your communication skills. The best degree post CA, without doubt.
b. CFA - The 'toughest exam of wall street'. It teaches you almost everything an MBA will or even more. You end up spending 10% of what you will if you do an MBA. Plus you can do it while you are working. However, it doesn't have any placement services. Also, you do not get to have the alumni advantage an MBA will give you.
c. FRM - Financial Risk Manager - A good degree to possess if you want to get into treasury or desire a banking job. Not very popular in the industry yet. The only advantage is less time to complete the course. It can be finished within 6 months. Also very cheap. Very technical though.
2. Accounting - In case you wish to get into practice
a. CPA, ACCA, CMA - Good additions if you want to pursue auditing or want to start your own firm. The biggest advantage of the trio is global appeal. It would be really beneficial if you plan to relocate post your qualification. No advantage if you want a career in finance.
b. CISA, DISA - If you wish to get into IT audits, CISA DISA is a great addition. You get to learn new skills. If not, do not even think about it.
3. CFE - Certified Fraud Examiner - Helps to land a job in the BIG 4 in the fraud investigation department. Makes you better prepared for a forensic audit role. The interviewer might give you extra brownie points if you are done with this certification.
4. Actuarial Science - CA and actuarial has become a popular career path these days. You see many people do both the degrees. However, I would suggest it only in case you intend to get into insurance. Also, it is advisable to do it full time. Actuary with office can be a tough ask.
5. Bcom, Mcom - Bcom,in my opinion is a must while doing CA. Most Bcom colleges do not demand attendance and hence are ideal while pursuing articleship. Mcom can be done in case you wish to go for an abroad MBA, to fulfil the 16 years of education criteria. Otherwise it will add absolutely zero value.
6. CS, LLB - Can be good additions in case you wish to advance your career in the corporate law department of a company.A past favourite of students, the CA+CS combo is being pursued by lesser people these days.
7. Insolvency Professional - With a surge in bad loans, being an insolvency professional is a nice opportunity for experienced CAs. With RBI strengthening provisioning norms, this profession is here to stay. You would need to have 10 years work experience and also pass an exam. It is a very niche field.
8. Tax practice - In case you want to make a career in tax, you really do not need any other degrees. There are few certificate courses offered by ICAI which you can do. However, not much value will be added.
All said and done, nothing beats a CA+MBA. The main skill a CA lacks is presentation and communication. An MBA would look to improve that and also provide a lucrative job. With IIMs focusing on increasing diversity, this is the best chance for CAs to get into the top B-schools of India!!