In vedic astrology there are remedies and mantras which provide immediate help. They are not long term solutions and need to be recited only when needed. Once the natives goal is fulfilled he/she may or may not need the mantra remedy. The effect from these mantra remedy is not permanent but sometimes the need arises for instant solutions. When in a pinch try these mantras to get a favorable result:

वक्रतुण्ड महाकाय सूर्यकोटि समप्रभ
निर्विघ्नं कुरु मे देव सर्वकार्येषु सर्वदा

Vakra-Tunndda Maha-Kaaya Suurya-Kotti Samaprabha
Nirvighnam Kuru Me Deva Sarva-Kaaryessu Sarvadaa

This Ganesha Mantra is a sure shot way to remove imediate obstacles that have popped up in your life. Just recite this in times of needs and a solution to obstacle would be available to you. Ofcourse don't expect the obstacle to remove itself. You have to do the hard work to remove the obstacle but solution would be visible by this mantra.

ओम् आंजनेयाय विद्मिहे वायुपुत्राय धीमहि तन्नो: हनुमान: प्रचोदयात

Om-Anjeneyay Vidhmahey Vayuputray Dhimahi Tanno Hanumanah Prachodayat

This is the Anjane Gayatri Mantra for Lord Hanuman. Hanuman is a servant of Lord Ram. Essentially job is a service for someone. So praying to Lord Hanuman is pre-requisite for any job seeker. Promotions needs some favor from Lord Ganesha but overall this Anjane Gayatri Mantra should suffice for all people looking for a job or promotion.

ॐ भूर्भुवः स्वः तत्सवितुर्वरेण्यं।
भर्गो देवस्य धीमहि धियो यो नः प्रचोदयात् ॥

Om Bhuur-Bhuvah Svah Tat-Savitur-Varennyam |
Bhargo Devasya Dhiimahi Dhiyo Yo Nah Pracodayaat ||

This is the Gayatri Mantra. This is the greatest mantra in Vedas. Even Krishna confessed of the greatness of Gayatri Mantra by saying He is Gayatri among the Mantras in Chapter 10 Sloka 35. Gayatri Mantra is better explained in the article: Power Of Mantras. When there are exams or when you need to focus for a long time at workplace then recitation of Gayatri Mantra is the best. Health also improves by recitation of Gayatri Mantra.  

सरस्वति महाभागे विद्ये कमललोचने ।
विद्यारूपे विशालाक्षि विद्यां देहि नमोस्तुते ॥

Sarasvati Mahaa-Bhaage Vidye Kamala-Locane |
Vidyaa-Ruupe Vishaal-Aakssi Vidyaam Dehi Namostute ||

या कुन्देन्दुतुषारहारधवला या शुभ्रवस्त्रावृता या वीणावरदण्डमण्डितकरा या श्वेतपद्मासना ।
या ब्रह्माच्युतशंकरप्रभृतिभिर्देवः सदा पूजिता सा मां पातु सरस्वति भगवती निःशेषजाड्यापहा ॥१॥

Yaa Kundeandu-Tussaara-Haara-Dhavalaa Yaa Shubhra-Vastraavrtaa Yaa Viinnaa-Vara-Dannda-Mannddita-Karaa Yaa Shveta-Padma-asanaa |
Yaa Brahma-Acyuta-Shankara-Prabhrtibhir-Devah Sadaa Puujitaa Saa Maam Paatu Sarasvati Bhagavatii Nihshessa-Jaaddya-Apahaa ||1||

The two mantras are hymns to Goddess Saraswati. Goddess Saraswati gives education and effective speech. Don't confuse education with knowledge. If you are looking for knowledge then prayers to forbidden God Lord Brahma or Lord Shiva are advised. If you want to acquire technical skills or to build something constructive then prayers to Lord Vishwakarma are a good option. 

ॐ श्रीं ह्रीं श्रीं कमले कमलालये प्रसीद प्रसीद ॐ श्रीं ह्रीं श्रीं महालक्ष्मयै नम:॥

Om Shreem Hreem Shreem Kamale Kamalalaye
Praseed Praseed Om Shreem Hreem Shreem Mahalaksh-myai Namah

The mantras for wealth and prosperity should be easily available on web so no point bothering to give them all. But this mantra has the potential to increase means of earning if spoken while observing The Shree Yantra. 

पत्नीं मनोरमां देहि मनोवृतानु सारिणीम् |
तारिणीम् दुर्ग संसार सागरस्य कुलोद्भवाम ||

Patnim  Manoramam Dehi Manovritanu Sarineem |

Tarineem Durg Sansar Sagarasya Kulodbhavaam ||

The ancient sages who wrote these mantras knew there would be people who would need such a mantra. So if your marriage is not happening and you are looking for a suitable bride this is a great mantra for you. The potential bride would be beautiful and source of happiness for the groom if the groom regularly recites this mantra until he gets married. 

कात्यायनि महामाये महायोगिन्यधीश्वरि ।
नन्द गोपसुतं देविपतिं मे कुरु ते नमः ॥

Katyayani Mahamaye Mahayoginyadheeshwari |
Nandgopsutam Devipatim Me Kuru te Namah ||

हे गौरि शंकरार्धांगि यथा त्वं शंकरप्रिया ।
तथा मां कुरु कल्याणि कान्तकातां सुदुर्लभाम ॥

Hey Gauri Shankarardhangi Yatha Tvam Shankarpriyaa |
Tatha Mam Kuru Kalyaani Kaantkatam Sudurlabhaam ||

These two mantras can fetch a worthy husband. Also praying to Shiva and Shiva Ling especially on a Monday and keeping a fast or eating only once has been known to provide a worthy and suitable husband to the potential bride. Praying to Shiva is the best option to fetch a suitable spouse for potential brides.

ॐ मृत्युंजयमहादेव त्राहि मां शरणागतम्‌।
जन्ममृत्युजरापीडितं कर्मबंधनैः॥

Om Mrityunjay Mahadev Trahima Sharnagatam
Janma Mrityu Jara Piditam Karmbandhanaiha

ॐत्र्यम्बकंयजामहे सुगन्धिंपुष्टिवर्धनम्
उर्वारुकमिवबन्धनान्मृ त्योर्मुक्षीयमामृतात् ॥

These are great mantras to remove fears be it real or imaginery. There are lot of people in present times who have phobia's, anxities and depression. A few people who tend to worry too much can also speak this mantra to remove fears and anxities. Once you feel normal then chant the sacred 'Om Namah Shivay' mantra to get the calmness back. 

   For any astrological or spiritual solution to work you need to have faith in that solution. If you don't believe that mantra would help than its no use reciting them.